# log4javascript

# log4javascript 1.4 manual

## Contents

- Introduction
- AMD
- Note about the log4javascript object
- Loggers, appenders, layouts and levels
  - Configuring appenders
  - Example
- log4javascript static properties/methods
- Levels
- Loggers
- Appenders
  - Appender
  - AlertAppender
  - AjaxAppender
  - PopUpAppender
  - InPageAppender
  - BrowserConsoleAppender
- Layouts
  - Layout
  - NullLayout
  - SimpleLayout
  - PatternLayout
  - XmlLayout
  - JsonLayout
  - HttpPostDataLayout
- Enabling / disabling log4javascript
- log4javascript error handling
  - LogLog
- Differences between log4javascript and log4j

## Introduction

log4javascript currently exists to provide more flexible and configurable JavaScript logging than that provided by browser developer tools. It works a very wide range of browsers. It was originally written to ease the pain of JavaScript debugging in the days before browsers came with advanced developer tools.

It requires only a JavaScript include and one line of code to initialize with default settings. Having for several years used log4j and its .NET port log4net, it was natural for me to base it on log4j.

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## AMD

Since version 1.4.10, log4javascript comes with AMD support hence can be loaded by a script loader such as RequireJS.

The current version of JavaScript is designed only to run in a browser. If not using AMD, log4javascript creates a single property of the global object (to all intents and purposes, a global variable) called `log4javascript`.

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## Note about the log4javascript object

All of log4javascript's instantiable classes are accessible via the log4javascript object, which acts as a namespace. Therefore references to all class names must be preceded with "log4javascript.". For example:

`var popUpAppender = new log4javascript.PopUpAppender();`

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## Loggers, Appenders, Layouts and Levels

A logger in log4javascript is the object on which log calls are made. A logger may be assigned zero or more appenders. An appender is an object that actually does the logging: for example, a `PopUpAppender` logs messages to a pop-up console window while an `AjaxAppender` uses HTTP to send log messages back to the server. Each appender is assigned a layout, which is responsible for formatting log messages that are passed to an appender.

Every log message has a level. This is the severity of the message. Available levels are `TRACE`, `DEBUG`, `INFO`, `WARN`, `ERROR` and `FATAL` - these correspond to the logging methods `trace`, `debug`, `info`, `warn`, `error` and `fatal` of `Logger`. Levels are ordered as follows: `TRACE` < `DEBUG` < `INFO` < `WARN` < `ERROR` < `FATAL`. This means the `FATAL` is the most severe and `TRACE` the least. Also included are levels called `ALL` and `OFF` intended to enable or disable all logging respectively.

Both loggers and appenders also have threshold levels (by default, `DEBUG` for loggers and `ALL` for appenders). Setting a level to either a logger or an appender disables log messages of severity lower than that level. For instance, if a level of `INFO` is set on a logger then only log messages of severity `INFO` or greater will be logged, meaning `DEBUG` and `TRACE` messages will not be logged. If the same logger had two appenders, one of level `DEBUG` and one of level `WARN` then the first appender will still only log messages of `INFO` or greater while the second appender will only log messages of level `WARN` or greater.

This allows the developer fine control over which messages get logged where.

### Configuring appenders

From version 1.4, configuring appenders is only possible via configuration methods. As the number of configuration options increases it becomes increasingly undesirable to use constructor parameters, so support for it has been dropped.

### Example

NB. The Ajax side of this example relies on having server-side processing in place.

First, log4javascript is initialized, and a logger (actually the anonymous logger) is assigned to a variable called `log`:

    <script type="text/javascript" src="log4javascript.js"></script>
    <script type="text/javascript">
        //<![CDATA[
        var log = log4javascript.getLogger();

`log` does not yet have any appenders, so a call to `log.debug()` will do nothing as yet. For this example we will use a `PopUpAppender` for debugging purposes. Since the lifespan of the messages displayed in the pop-up is only going to be the same as that of the window, a `PatternLayout` is used that displays the time of the message and not the date (note that this is also true of PopUpAppender's default layout). The format of the string passed into PatternLayout is explained below.

        var popUpAppender = new log4javascript.PopUpAppender();
        var popUpLayout = new log4javascript.PatternLayout("%d{HH:mm:ss} %-5p - %m%n");
        popUpAppender.setLayout(popUpLayout);
        log.addAppender(popUpAppender);

Suppose that we also want to send log messages to the server, but limited to error messages only. To achieve this we use an `AjaxAppender`. Note that if no layout is specified then for convenience a default layout is used; in the case of AjaxAppender, that is `HttpPostDataLayout`, which formats log messages as a standard HTTP POST string from which a simple server-side script (not provided with log4javascript) will be able to extract posted parameters. This is fine for our purposes:

        var ajaxAppender = new log4javascript.AjaxAppender("myloggingservlet.do");
        ajaxAppender.setThreshold(log4javascript.Level.ERROR);
        log.addAppender(ajaxAppender);

Finally, some test log messages and the closing script tag:

        log.debug("Debugging message (appears in pop-up)");
        log.error("Error message (appears in pop-up and in server log)");
        //]]>
    </script>

The full script:

    <script type="text/javascript" src="log4javascript.js"></script>
    <script type="text/javascript">
        //<![CDATA[
        var log = log4javascript.getLogger();
        var popUpAppender = new log4javascript.PopUpAppender();
        var popUpLayout = new log4javascript.PatternLayout("%d{HH:mm:ss} %-5p - %m%n");
        popUpAppender.setLayout(popUpLayout);
        log.addAppender(popUpAppender);
        var ajaxAppender = new log4javascript.AjaxAppender("myloggingservlet.do");
        ajaxAppender.setThreshold(log4javascript.Level.ERROR);
        log.addAppender(ajaxAppender);
        log.debug("Debugging message (appears in pop-up)");
        log.error("Error message (appears in pop-up and in server log)");
        //]]>
    </script>

See this example in action (opens in new window)

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## log4javascript static properties/methods

#### Properties

- version
  The version number of your copy of log4javascript.
- edition
  The edition of your copy of log4javascript.
- logLog
  log4javascript's internal logging object. See below for more details.

#### Methods

- getLogger
  `Logger getLogger([String loggerName])`
  Parameters:
  - `loggerName` [optional]

  Returns a logger with the specified name, creating it if a logger with that name does not already exist. If no name is specified, a logger is returned with name `[anonymous]`, and subsequent calls to `getLogger()` (with no logger name specified) will return this same logger object.

  Note that the names `[anonymous]`, `[default]`, `[null]` and `root` are reserved for the anonymous logger, default logger, null logger and root logger respectively.

- getDefaultLogger
  `Logger getDefaultLogger()`

  Convenience method that returns the default logger. In the standard edition, the default logger has a single appender: a `PopUpAppender` with the default layout, width and height, and with `focusPopUp` set to false and `lazyInit`, `useOldPopUp` and `complainAboutPopUpBlocking` all set to true.

  In the production edition, the default logger has no appenders.

- getNullLogger
  `Logger getNullLogger()`
  Returns an empty logger with no appenders. Useful for disabling all logging.
- getRootLogger
  `Logger getRootLogger()`
  Returns the root logger from which all other loggers derive.
- resetConfiguration
  `void resetConfiguration()`
  Resets the all loggers to their default level.
- setEnabled
  `void setEnabled(Boolean enabled)`
  Parameters:
  - `enabled`
  Enables or disables all logging, depending on `enabled`.
- isEnabled
  `Boolean isEnabled()`
  Returns true or false depending on whether logging is enabled.
- addEventListener
  `void addEventListener(String eventType, Function listener)`
  Parameters:
  - `eventType`
  - `listener`

  Adds a function to be called when an event of the type specified occurs in log4javascript. Supported event types are `load` (occurs once the page has loaded) and `error`.

  Each listener is pased three paramaters:

  - `sender`. The object that raised the event (i.e. the log4javascript object);
  - `eventType`. The type of the event;
  - `eventArgs`. An object containing of event-specific arguments. For the `error` event, this is an object with properties `message` and `exception`. For the `load` event this is an empty object.
- removeEventListener
  `void removeEventListener(String eventType, Function listener)`
  Parameters:
  - `eventType`
  - `listener`
  Removes the event listener function supplied for the event of the type specified.
- dispatchEvent
  `void dispatchEvent(String eventType, Object eventArgs)`
  Parameters:
  - `eventType`
  - `eventArgs`
  Raises an event of type `eventType` on the `log4javascript` object. Each of the listeners for this type of event (registered via `addEventListener`) is called and passed `eventArgs` as the third parameter.
- setEventTypes
  `void setEventTypes(Array eventTypes)`
  Parameters:
  - `eventTypes`
  Used internally to specify the types of events that the `log4javascript` object can raise.
- setShowStackTraces
  `void setShowStackTraces(Boolean show)`
  Parameters:
  - `show`
  Enables or disables displaying of error stack traces, depending on `show`. By default, stack traces are not displayed. (Only works in Firefox)
- evalInScope
  `Object evalInScope(String expr)`
  Parameters:
  - `expr`
  This evaluates the given expression in the log4javascript scope, thus allowing scripts to access internal log4javascript variables and functions. This was written for the purposes of automated testing but could be used by custom extensions to log4javascript.

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## Levels

Levels are available as static properties of the `log4javascript.Level` object. In ascending order of severity:

1. `log4javascript.Level.ALL`
2. `log4javascript.Level.TRACE`
3. `log4javascript.Level.DEBUG`
4. `log4javascript.Level.INFO`
5. `log4javascript.Level.WARN`
6. `log4javascript.Level.ERROR`
7. `log4javascript.Level.FATAL`
8. `log4javascript.Level.OFF`

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## Loggers

It is possible to have multiple loggers in log4javascript. For example, you may wish to have a logger for debugging purposes that logs messages to a pop-up window and a separate logger that reports any client-side application errors to the server via Ajax.

### Logger hierarchy and appender additivity

From version 1.4, log4javascript has hierarchical loggers, implemented in the same way as log4j. In summary, you specify a logger's parent logger by means of a dot between the parent logger name and the child logger name. Therefore the logger `tim.app.security` inherits from `tim.app`, which in turn inherits from `tim` which, finally, inherits from the root logger.

What inheritance means for a logger is that in the absence of a threshold level set specifically on the logger it inherits its level from its parent; also, a logger inherits all its parent's appenders (this is known as appender additivity in log4j. This behaviour can be enabled or disabled via `setAdditivity()`. See below). In the above example, if the root logger has a level of `DEBUG` and one appender, each of the loggers `tim.app.security`, `tim.app` and `tim` would inherit the root level's appender. If, say, `tim.app`'s threshold level was set to `WARN`, `tim`'s effective level would remain at `DEBUG` (inherited from the root logger) while `tim.app.security`'s effective level would be `WARN`, inherited from `tim.app`. The important thing to note is that appenders accumulate down the logger hierarchy while levels are simply inherited from the nearest ancestor with a threshold level set.

For a detailed explanation of the logger hierarchy, see the log4j manual.

Notes

- It is not possible to instantiate loggers directly. Instead you must use one of the methods of the `log4javascript` object: `getLogger`, `getRootLogger`, `getDefaultLogger` or `getNullLogger`.

#### Logger methods

- addAppender
  `void addAppender(Appender appender)`
  Parameters:
  - `appender`
  Adds the given appender.
- removeAppender
  `void removeAppender(Appender appender)`
  Parameters:
  - `appender`
  Removes the given appender.
- removeAllAppenders
  `void removeAllAppenders()`
  Clears all appenders for the current logger.
- setLevel
  `void setLevel(Level level)`
  Parameters:
  - `level`
  Sets the level. Log messages of a lower level than `level` will not be logged. Default value is `DEBUG`.
- getLevel
  `Level getLevel()`
  Returns the level explicitly set for this logger or `null` if none has been set.
- getEffectiveLevel
  `Level getEffectiveLevel()`
  Returns the level at which the logger is operating. This is either the level explicitly set on the logger or, if no level has been set, the effective level of the logger's parent.
- setAdditivity
  `void setAdditivity(Boolean additivity)`
  Parameters:
  - `additivity`

  Sets whether appender additivity is enabled (the default) or disabled. If set to false, this particular logger will not inherit any appenders form its ancestors. Any descendant of this logger, however, will inherit from its ancestors as normal, unless its own additivity is explicitly set to false.

  Default value is `true`.

- getAdditivity
  `Boolean getAdditivity()`
  Returns whether additivity is enabled for this logger.
- log
  `void log(Level level, Object params)`
  Parameters:
  - `level`
  - `params`
  Generic logging method used by wrapper methods such as `debug`, `error` etc.

  Notes

  - The signature of this method has changed in 1.4.
- trace
  `void trace(Object message1[, Object message2, ... ][, Error exception])`
  Parameters:
  - `message1[, message2...]`
  - `exception` [optional]
  Logs one or more messages and optionally an error at level `TRACE`.

  Notes

  - Logging of multiple messages in one call is new in 1.4.
- debug
  `void debug(Object message1[, Object message2, ... ][, Error exception])`
  Parameters:
  - `message1[, message2...]`
  - `exception` [optional]
  Logs one or more messages and optionally an error at level `DEBUG`.

  Notes

  - Logging of multiple messages in one call is new in 1.4.
- info
  `void info(Object message1[, Object message2, ... ][, Error exception])`
  Parameters:
  - `message1[, message2...]`
  - `exception` [optional]
  Logs one or more messages and optionally an error at level `INFO`.

  Notes

  - Logging of multiple messages in one call is new in 1.4.
- warn
  `void warn(Object message1[, Object message2, ... ][, Error exception])`
  Parameters:
  - `message1[, message2...]`
  - `exception` [optional]
  Logs one or more messages and optionally an error at level `WARN`.

  Notes

  - Logging of multiple messages in one call is new in 1.4.
- error
  `void error(Object message1[, Object message2, ... ][, Error exception])`
  Parameters:
  - `message1[, message2...]`
  - `exception` [optional]
  Logs one or more messages and optionally an error at level `ERROR`.

  Notes

  - Logging of multiple messages in one call is new in 1.4.
- fatal
  `void fatal(Object message1[, Object message2, ... ][, Error exception])`
  Parameters:
  - `message1[, message2...]`
  - `exception` [optional]
  Logs one or more messages and optionally an error at level `FATAL`.

  Notes

  - Logging of multiple messages in one call is new in 1.4.
- isEnabledFor
  `Boolean isEnabledFor(Level level, Error exception)`
  Parameters:
  - `level`
  Returns whether the logger is enabled for the specified level.
- isTraceEnabled
  `Boolean isTraceEnabled()`
  Returns whether the logger is enabled for `TRACE` messages.
- isDebugEnabled
  `Boolean isDebugEnabled()`
  Returns whether the logger is enabled for `DEBUG` messages.
- isInfoEnabled
  `Boolean isInfoEnabled()`
  Returns whether the logger is enabled for `INFO` messages.
- isWarnEnabled
  `Boolean isWarnEnabled()`
  Returns whether the logger is enabled for `WARN` messages.
- isErrorEnabled
  `Boolean isErrorEnabled()`
  Returns whether the logger is enabled for `ERROR` messages.
- isFatalEnabled
  `Boolean isFatalEnabled()`
  Returns whether the logger is enabled for `FATAL` messages.
- group
  `void group(String name, Boolean initiallyExpanded)`
  Parameters:
  - `name`
  - `initiallyExpanded` [optional]
  Starts a new group of log messages. In appenders that support grouping (currently `PopUpAppender` and `InPageAppender`), a group appears as an expandable section in the console, labelled with the `name` specified. Specifying `initiallyExpanded` determines whether the group starts off expanded (the default is `true`). Groups may be nested.
- groupEnd
  `void groupEnd()`
  Ends the current group. If there is no group then this function has no effect.
- time
  `void time(String name, Level level)`
  Parameters:
  - `name`
  - `level` [optional]
  Starts a timer with name `name`. When the timer is ended with a call to `timeEnd` using the same name, the amount of time that has elapsed in milliseconds since the timer was started is logged at level `level`. If not level is supplied, the level defaults to `INFO`.
- timeEnd
  `void timeEnd(String name)`
  Parameters:
  - `name`
  Ends the timer with name `name` and logs the time elapsed.
- assert
  `void assert(Object expr)`
  Parameters:
  - `expr`
  Asserts the given expression is `true` or evaluates to `true`. If so, nothing is logged. If not, an error is logged at the `ERROR` level.

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## Appenders

### Appender

There are methods common to all appenders, as listed below.

#### Methods

- doAppend
  `void doAppend(LoggingEvent loggingEvent)`
  Parameters:
  - `loggingEvent`

  Checks the logging event's level is at least as severe as the appender's threshold and calls the appender's `append` method if so.

  This method should not in general be used directly or overridden.

- append
  `void append(LoggingEvent loggingEvent)`
  Parameters:
  - `loggingEvent`
  Appender-specific method to append a log message. Every appender object should implement this method.
- setLayout
  `void setLayout(Layout layout)`
  Parameters:
  - `layout`
  Sets the appender's layout.
- getLayout
  `Layout getLayout()`
  Returns the appender's layout.
- setThreshold
  `void setThreshold(Level level)`
  Parameters:
  - `level`
  Sets the appender's threshold. Log messages of level less severe than this threshold will not be logged.
- getThreshold
  `Level getThreshold()`
  Returns the appender's threshold.
- toString
  `string toString()`
  Returns a string representation of the appender. Every appender object should implement this method.

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### AlertAppender

Editions: Standard

Displays a log message as a JavaScript alert.

#### Constructor

- AlertAppender
  `AlertAppender()`

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### AjaxAppender

Editions: Standard, Production

A flexible appender that asynchronously sends log messages to a server via HTTP.

The default configuration is to send each log message as a separate HTTP post request to the server using an `HttpPostDataLayout`, without waiting for a response before sending any subsequent requests. However, an `AjaxAppender` may be configured to do any one of or combinations of the following:

- send log messages in batches (if the selected layout supports it - particularly suited to `AjaxAppender` are `JsonLayout` and `XmlLayout`, both of which allow batching);
- wait for a response from a previous request before sending the next log message / batch of messages;
- send all queued log messages at timed intervals.

Notes

- AjaxAppender relies on the `XMLHttpRequest` object. It also requires the presence of correctly implemented `setRequestHeader` method on this object, which rules out Opera prior to version 8.01. If your browser does not support the necessary objects then one alert will display to explain why it doesn't work, after which the appender will silently switch off.
- In AjaxAppender only, `setLayout` may not be called after the first message has been logged.
- The default layout is `HttpPostDataLayout`.

- From version 1.4, log message data is always sent as one or more name/value pairs. In the case of `HttpPostDataLayout`, data is sent the same as in previous versions. For other layouts such as `JsonLayout` and `XmlLayout`, the formatted log message is posted as the value of a parameter called `data`, though this may be changed via `setPostVarName`.

  From version 1.4.5, it is possible to override this behaviour so that logging data is sent as the request payload rather than as a posted form variable. This is done by setting the `Content-Type` header sent with each Ajax request explicitly. For example, if using a `JsonLayout`:

      ajaxApender.addHeader("Content-Type", "application/json");

- From version 1.4, log message timestamps are sent as standard JavaScript times, i.e. the number of milliseconds since 00:00:00 UTC on January 1, 1970.

- Also from version 1.4, any outstanding log messages may optionally be sent when the main page unloads (i.e. user follows a link, closes the window or refreshes the page). This behaviour may be enabled using `setSendAllOnUnload`; see below.

  This behaviour is dependent on `window.onbeforeunload`; unfortunately, Opera does not always raise this event, so this feature does not work reliably in Opera.

- From version 1.4.8, AjaxAppender supports the sending of cookies in CORS requests via the new `withCredentials` constructor parameter.

#### Constructor

- AjaxAppender
  `AjaxAppender(String url[, Boolean withCredentials])`
  Parameters:
  - `url`
    The URL to which log messages should be sent. Note that this is subject to the usual Ajax restrictions: the URL should be in the same domain as that of the page making the request.
  - `withCredentials`

    Since: 1.4.8

    Specifies whether cookies should be sent with each request.

#### Methods

- setSendAllOnUnload
  `void setSendAllOnUnload(Boolean sendAllOnUnload)`

  [not available after first message logged]

  Whether to send all remaining unsent log messages to the server when the page unloads.

  Since version 1.4.3, the default value is `false`. Previously the default was `true`.

  Notes

  - This feature was found not to work prior to version 1.4.3 in WebKit browsers (e.g. Google Chrome, Safari). As a result, a workaround was implemented in 1.4.3 which has the unfortunate side effect of popping up a confirmation dialog to the user if there are any log messages to send when the page unloads. As a result, this feature is now obtrusive for the user and is therefore disabled by default.
  - This feature does not work in any version of Opera.
- isSendAllOnUnload
  `Boolean isSendAllOnUnload()`
  Returns whether all remaining unsent log messages are sent to the server when the page unloads.
- setPostVarName
  `void setPostVarName(String postVarName)`

  [not available after first message logged]

  Sets the post variable name whose value will the formatted log message(s) for each request.

  Default value is `data`.

  Notes

  - This has no effect if the current layout is an `HttpPostDataLayout`.
- getPostVarName
  `String getPostVarName()`
  Returns the post variable name whose value will the formatted log message(s) for each request.
- setTimed
  `void setTimed(Boolean timed)`

  [not available after first message logged]

  Whether to send log messages to the server at regular, timed intervals.

  Default value is `false`.

- isTimed
  `Boolean isTimed()`
  Returns whether log messages are sent to the server at regular, timed intervals.
- setWaitForResponse
  `void setWaitForResponse(Boolean waitForResponse)`

  [not available after first message logged]

  Sets whether to wait for a response from a previous HTTP request from this appender before sending the next log message / batch of messages.

  Default value is `false`.

- isWaitForResponse
  `Boolean isWaitForResponse()`
  Returns whether the appender waits for a response from a previous HTTP request from this appender before sending the next log message / batch of messages.
- setBatchSize
  `void setBatchSize(Number batchSize)`

  [not available after first message logged]

  Sets the number of log messages to send in each request. If not specified, defaults to `1`.

  Notes

  - Setting this to a number greater than 1 means that the appender will wait until it has forwarded that many valid log messages before sending any more. This also means that if the page unloads for any reason and `sendAllOnUnload` is not set to `true`, any log messages waiting in the queue will not be sent.
  - If batching is used in conjunction with timed sending of log messages, messages will still be sent in batches of size `batchSize`, regardless of how many log messages are queued by the time the timed sending is invoked. Incomplete batches will not be sent except when the page unloads, if `sendAllOnUnload` is set to `true`.
- getBatchSize
  `Number getBatchSize()`
  Returns the number of log messages sent in each request. See above for more details.
- setTimerInterval
  `void setTimerInterval(Number timerInterval)`

  [not available after first message logged]

  Sets the length of time in milliseconds between each sending of queued log messages.

  Notes

  - `timerInterval` only has an effect in conjunction with `timed` (set by `setTimed()`. If `timed` is set to false then `timerInterval` has no effect.
  - Each time the queue of log messages or batches of messages is cleared, the countdown to the next sending only starts once the final request has been sent (and, if `waitForResponse` is set to `true`, the final response received). This means that the actual interval at which the queue of messages is cleared cannot be fixed.
- getTimerInterval
  `Number getTimerInterval()`
  Returns the length of time in milliseconds between each sending of queued log messages. See above for more details.
- setRequestSuccessCallback
  `void setRequestSuccessCallback(Function requestSuccessCallback)`

  Sets the function that is called whenever a successful request is made, called at the point at which the response is received. This feature can be used to confirm whether a request has been successful and act accordingly.

  A single parameter, `xmlHttp`, is passed to the callback function. This is the XMLHttpRequest object that performed the request.

- setFailCallback
  `void setFailCallback(Function failCallback)`

  Sets the function that is called whenever any kind of failure occurs in the appender, including browser deficiencies or configuration errors (e.g. supplying a non-existent URL to the appender). This feature can be used to handle AjaxAppender-specific errors.

  A single parameter, `message`, is passed to the callback function. This is the error-specific message that caused the failure.

- setSessionId
  `void setSessionId(String sessionId)`
  Sets the session id sent to the server each time a request is made.
- getSessionId
  `String getSessionId()`
  Returns the session id sent to the server each time a request is made.
- addHeader
  `void addHeader(String name, String value)`

  Adds an HTTP header that is sent with each request.

  Since: 1.4.3

  From 1.4.5, specifying the `Content-Type` header using this method will force logging data to be sent as the Ajax request payload rather than as a posted form field.

- getHeaders
  `Array getHeaders()`
  Returns an array of the additional headers that are sent with each HTTP request. Each array item is an object with properties `name` and `value`.

  Since: 1.4.3

- sendAll
  `void sendAll()`
  Sends all log messages in the queue. If log messages are batched then only completed batches are sent.

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### PopUpAppender

Editions: Standard

Logs messages to a pop-up console window (note: you will need to disable pop-up blockers to use it). The pop-up displays a list of all log messages, and has the following features:

- log messages are colour-coded by severity;
- log messages are displayed in a monospace font to allow easy readability;
- switchable wrap mode to allow wrapping of long lines
- all whitespace in log messages is honoured (except in wrap mode);
- filters to show and hide messages of a particular level;
- search facility that allows searching of log messages as you type, with the following features:
  - supports regular expressions;
  - case sensitive or insensitive matching;
  - buttons to navigate through all the matches;
  - switch to highlight all matches;
  - switch to filter out all log messages that contain no matches;
  - switch to enable or disable the search;
  - search is dynamically applied to every log message as it is added to the console.
- switch to toggle between logging from the top down and from the bottom up;
- switch to turn automatic scrolling when a new message is logged on and off;
- switch to turn off all logging to the pop-up (useful if a timer is generating unwanted log messages);
- optional configurable limit to the number of log message that are displayed. If set and this limit is reached, each new log message will cause the oldest one to be discarded;
- grouped log messages. Groups may be nested and each has a button to show or hide the log messages in that group;
- clear button to allow user to delete all current log messages.
- command prompt with up/down arrow history. Command line functions may be added to the appender. Several command line functions are built in:
  - `$(String id)`
    Prints a string representation of a single element with the id supplied.
  - `dir(Object obj)`
    Prints a list of a properties of the object supplied.
  - `dirxml(HTMLElement el)`
    Prints the XML source code of an HTML or XML element
  - `cd(Object win)`
    Changes the scope of execution of commands to the named frame or window (either a window/frame name or a reference to a window object may be supplied).
  - `clear()`
    Clears the console.
  - `keys(Object obj)`
    Prints a list of the names of all properties of the object supplied.
  - `values(Object obj)`
    Prints a list of the values of all properties of the object supplied.
  - `expansionDepth(Number depth)`
    Sets the number of levels of expansion of objects that are displayed by the command line. The default value is 1.

Notes

- The default layout for this appender is `PatternLayout` with pattern string

  `%d{HH:mm:ss} %-5p - %m{1}%n`

#### Constructor

- PopUpAppender
  `PopUpAppender([Boolean lazyInit, Boolean initiallyMinimized, Boolean useDocumentWrite, Number width, Number height])`
  Parameters:
  - `lazyInit` [optional]
    Set this to `true` to open the pop-up only when the first log message reaches the appender. Otherwise, the pop-up window opens as soon as the appender is created. If not specified, defaults to `false`.
  - `initiallyMinimized` [optional]

    Whether the console window should start off hidden / minimized. If not specified, defaults to `false`.

  - `useDocumentWrite` [optional]

    Specifies how the console window is created. By default, the console window is created dynamically using `document`'s `write` method. This has the advantage of keeping all the code in one single JavaScript file. However, if your page sets `document.domain` then the browser prevents script access to a window unless it too has the same value set for `document.domain`. To get round this issue, you can set `useDocumentWrite` to `false` and log4javascript will instead use the external HTML file `console.html` (or `console_uncompressed.html` if you're using an uncompressed version of log4javascript.js), which must be placed in the same directory as your log4javascript.js file.

    Note that if `useDocumentWrite` is set to `true`, the old pop-up window will always be closed and a new one created whenever the page is refreshed, even if `setUseOldPopUp(true)` has been called.

    In general it's simpler to use the `document.write` method, so unless your page needs to set `document.domain`, `useDocumentWrite` should be set to `true`.

    If not specified, defaults to `true`.

  - `width` [optional]
    The outer width in pixels of the pop-up window. If not specified, defaults to `600`.
  - `height` [optional]
    The outer height in pixels of the pop-up window. If not specified, defaults to `400`.

#### Methods

- isInitiallyMinimized
  `Boolean isInitiallyMinimized()`
  Returns whether the console window starts off hidden / minimized.
- setInitiallyMinimized
  `void setInitiallyMinimized(Boolean initiallyMinimized)`
  [not available after initialization]
  Sets whether the console window should start off hidden / minimized.
- isFocusPopUp
  `Boolean isFocusPopUp()`
  Returns whether the pop-up window is focussed (i.e. brought it to the front) when a new log message is added. Default value is `false`.
- setFocusPopUp
  `void setFocusPopUp(Boolean focusPopUp)`
  Sets whether to focus the pop-up window (i.e. bring it to the front) when a new log message is added.
- isUseOldPopUp
  `Boolean isUseOldPopUp()`

  Returns whether the same pop-up window is used if the main page is reloaded. If set to `true`, when the page is reloaded a line is drawn in the pop-up and subsequent log messages are added to the same pop-up. Otherwise, a new pop-up window is created that replaces the original pop-up. If not specified, defaults to `true`.

  Notes

  - In Internet Explorer 5, the browser prevents this from working properly, so a new pop-up window is always created when the main page reloads. Also, the original pop-up does not get closed.
- setUseOldPopUp
  `void setUseOldPopUp(Boolean useOldPopUp)`
  [not available after initialization]
  Sets whether to use the same pop-up window if the main page is reloaded. See `isUseOldPopUp` above for details.
- isComplainAboutPopUpBlocking
  `Boolean isComplainAboutPopUpBlocking()`
  Returns whether an alert is shown to the user when the pop-up window cannot be created as a result of a pop-up blocker. Default value is `true`.
- setComplainAboutPopUpBlocking
  `void setComplainAboutPopUpBlocking(Boolean complainAboutPopUpBlocking)`
  [not available after initialization]
  Sets whether to announce to show an alert to the user when the pop-up window cannot be created as a result of a pop-up blocker.
- isNewestMessageAtTop
  `Boolean isNewestMessageAtTop()`
  Returns whether new log messages are displayed at the top of the pop-up window. Default value is `false` (i.e. log messages are appended to the bottom of the window).
- setNewestMessageAtTop
  `void setNewestMessageAtTop(Boolean newestMessageAtTop)`
  Sets whether to display new log messages at the top inside the pop-up window.
- isScrollToLatestMessage
  `Boolean isScrollToLatestMessage()`
  Returns whether the pop-up window scrolls to display the latest log message when a new message is logged. Default value is `true`.
- setScrollToLatestMessage
  `void setScrollToLatestMessage(Boolean scrollToLatestMessage)`
  Sets whether to scroll the pop-up window to display the latest log message when a new message is logged.
- isReopenWhenClosed
  `Boolean isReopenWhenClosed()`
  Returns whether the pop-up window reopens automatically after being closed when a new log message is logged. Default value is `false`.
- setReopenWhenClosed
  `void setReopenWhenClosed(Boolean reopenWhenClosed)`
  Sets whether to reopen the pop-up window automatically after being closed when a new log message is logged.
- getWidth
  `Number getWidth()`
  Returns the outer width in pixels of the pop-up window.
- setWidth
  `void setWidth(Number width)`
  [not available after initialization]
  Sets the outer width in pixels of the pop-up window.
- getHeight
  `Number getHeight()`
  [not available after initialization]
  Returns the outer height in pixels of the pop-up window.
- setHeight
  `void setHeight(Number height)`
  Sets the outer height in pixels of the pop-up window.
- getMaxMessages
  `Number getMaxMessages()`
  Returns the largest number of log messages that are displayed and stored by the the console. Once reached, a new log message wil cause the oldest message to be discarded. Default value is `null`, which means no limit is applied.
- setMaxMessages
  `void setMaxMessages(Number maxMessages)`
  [not available after initialization]
  Sets the largest number of messages displayed and stored by the console window. Set this to `null` to make this number unlimited.
- isShowCommandLine
  `Boolean isShowCommandLine()`
  Returns whether the console includes a command line. Default value is `true`.
- setShowCommandLine
  `void setShowCommandLine(Boolean showCommandLine)`
  Sets whether the console includes a command line.
- getCommandLineObjectExpansionDepth
  `Number getCommandLineObjectExpansionDepth()`
  Returns the number of levels to expand when an object value is logged to the console. Each property of an object above this threshold will be expanded if it is itself an object or array, otherwise its string representation will be displayed. Default value is 1 (i.e. the properties of the object logged will be displayed in their string representation but not expanded).
- setCommandLineObjectExpansionDepth:
  `void setCommandLineObjectExpansionDepth(Number expansionDepth)`
  Sets the number of levels to expand when an object value is logged to the console.
- getCommandWindow
  `Window getCommandWindow()`
  Returns a reference to the window in which commands typed into the command line are currently being executed.
- setCommandWindow
  `void setCommandWindow(Window commandWindow)`
  Sets the window in which commands typed into the command line are executed.
- getCommandLayout
  `Number getCommandLayout()`
  Returns the layout used to format the output for commands typed into the command line. The default value is a `PatternLayout` with pattern string `%m`
- setCommandLayout
  `void setCommandLayout(Layout commandLayout)`
  Sets the layout used to format the output for commands typed into the command line.
- clear
  `void clear()`
  Clears all messages from the console window.
- close
  `void close()`
  Closes the pop-up window.
- show
  `void show()`
  Opens the pop-up window, if not already open.
- hide
  `void hide()`
  Closes the pop-up window.
- focus
  `void focus()`
  Brings the console window to the top and gives it the focus.
- focusCommandLine
  `void focusCommandLine()`
  Brings the console window to the top and gives the focus to the command line.
- focusSearch
  `void focusSearch()`
  Brings the console window to the top and gives the focus to the search box.
- evalCommandAndAppend
  `void evalCommandAndAppend(String expr)`
  Evaluates the expression and appends the result to the console.
- addCommandLineFunction
  `void addCommandLineFunction(String functionName, Function commandLineFunction)`

  Adds a function with the name specified to the list of functions available on the command line. This feature may be used to add custom functions to the command line.

  When you call the function on the command line, `commandLineFunction` is executed with the following three parameters:

  - appender. A reference to the appender in which the command was executed;
  - args. An array-like list of parameters passed into the function on the command line (actually a reference to the `arguments` object representing the parameters passed into the function by the user);
  - returnValue. This is an object with two properties that allow the function to control how the result is displayed:
    - appendResult. A boolean value that determines whether the returned value from this function is appended to the console. The default value is `true`;
    - isError. A boolean value that specifies whether the output of this function should be displayed as an error. The default value is `false`.

  The value returned by the function is formatted by the command layout and appended to the console.

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### InPageAppender

Editions: Standard

Logs messages to a console window in the page. The console is identical to that used by the `PopUpAppender`, except for the absence of a 'Close' button.

Notes

- Prior to log4javascript 1.3, InPageAppender was known as InlineAppender. For the sake of backwards compatibility, InlineAppender is still included in 1.3 and later as an alias for InPageAppender.

- The default layout for this appender is `PatternLayout` with pattern string

  `%d{HH:mm:ss} %-5p - %m{1}%n`

#### Constructor

- InPageAppender
  `InPageAppender(HTMLElement container[, Boolean lazyInit, Boolean initiallyMinimized, Boolean useDocumentWrite, String width, String height])`
  Parameters:
  - `container`
    The container element for the console window. This should be an HTML element.
  - `lazyInit` [optional]
    Set this to `true` to create the console only when the first log message reaches the appender. Otherwise, the console is initialized as soon as the appender is created. If not specified, defaults to `true`.
  - `initiallyMinimized` [optional]

    Whether the console window should start off hidden / minimized. If not specified, defaults to `false`.

    Notes

    - In Safari (and possibly other browsers) hiding an `iframe` resets its document, thus destroying the console window.
  - `useDocumentWrite` [optional]

    Specifies how the console window is created. By default, the console window is created dynamically using `document`'s `write` method. This has the advantage of keeping all the code in one single JavaScript file. However, if your page sets `document.domain` then the browser prevents script access to a window unless it too has the same value set for `document.domain`. To get round this issue, you can set `useDocumentWrite` to `false` and log4javascript will instead use the external HTML file `console.html` (or `console_uncompressed.html` if you're using an uncompressed version of log4javascript.js), which must be placed in the same directory as your log4javascript.js file.

    In general it's simpler to use the `document.write` method, so unless your page needs to set `document.domain`, `useDocumentWrite` should be set to `true`.

    If not specified, defaults to `true`.

  - `width` [optional]
    The width of the console window. Any valid CSS length may be used. If not specified, defaults to `100%`.
  - `height` [optional]
    The height of the console window. Any valid CSS length may be used. If not specified, defaults to `250px`.

#### Methods

- addCssProperty
  `void addCssProperty(String name, String value)`
  Sets a CSS style property on the HTML element containing the console iframe.
- isVisible
  `Boolean isVisible()`
  Returns whether the console window is currently visible.
- isInitiallyMinimized
  `Boolean isInitiallyMinimized()`
  Returns whether the console window starts off hidden / minimized.
- setInitiallyMinimized
  `void setInitiallyMinimized(Boolean initiallyMinimized)`
  [not available after initialization]
  Sets whether the console window should start off hidden / minimized.
- isNewestMessageAtTop
  `Boolean isNewestMessageAtTop()`
  Returns whether new log messages are displayed at the top of the console window.
- setNewestMessageAtTop
  `void setNewestMessageAtTop(Boolean newestMessageAtTop)`
  Sets whether to display new log messages at the top inside the console window.
- isScrollToLatestMessage
  `Boolean isScrollToLatestMessage()`
  Returns whether the pop-up window scrolls to display the latest log message when a new message is logged.
- setScrollToLatestMessage
  `void setScrollToLatestMessage(Boolean scrollToLatestMessage)`
  Sets whether to scroll the console window to display the latest log message when a new message is logged.
- getWidth
  `String getWidth()`
  Returns the outer width of the console window.
- setWidth
  `void setWidth(String width)`
  [not available after initialization]
  Sets the outer width of the console window. Any valid CSS length may be used.
- getHeight
  `String getHeight()`
  Returns the outer height of the console window.
- setHeight
  `void setHeight(String height)`
  [not available after initialization]
  Sets the outer height of the console window. Any valid CSS length may be used.
- getMaxMessages
  `Number getMaxMessages()`
  Returns the largest number of messages displayed and stored by the console window.
- setMaxMessages
  `void setMaxMessages(Number maxMessages)`
  [not available after initialization]
  Sets the largest number of messages displayed and stored by the console window. Set this to `null` to make this number unlimited.
- isShowCommandLine
  `Boolean isShowCommandLine()`
  Returns whether the console includes a command line. Default value is `true`.
- setShowCommandLine
  `void setShowCommandLine(Boolean showCommandLine)`
  Sets whether the console includes a command line.
- getCommandLineObjectExpansionDepth
  `Number getCommandLineObjectExpansionDepth()`
  Returns the number of levels to expand when an object value is logged to the console. Each property of an object above this threshold will be expanded if it is itself an object or array, otherwise its string representation will be displayed. Default value is 1 (i.e. the properties of the object logged will be displayed in their string representation but not expanded).
- setCommandLineObjectExpansionDepth:
  `void setCommandLineObjectExpansionDepth(Number expansionDepth)`
  Sets the number of levels to expand when an object value is logged to the console.
- getCommandWindow
  `Window getCommandWindow()`
  Returns a reference to the window in which commands typed into the command line are currently being executed.
- setCommandWindow
  `void setCommandWindow(Window commandWindow)`
  Sets the window in which commands typed into the command line are executed.
- getCommandLayout
  `Number getCommandLayout()`
  Returns the layout used to format the output for commands typed into the command line. The default value is a `PatternLayout` with pattern string `%m`
- setCommandLayout
  `void setCommandLayout(Layout commandLayout)`
  Sets the layout used to format the output for commands typed into the command line.
- clear
  `void clear()`
  Clears all messages from the console window.
- show
  `void show()`

  Shows / unhides the console window.

  Notes

  - In Safari (and possibly other browsers), hiding an `iframe` resets its document, thus destroying the console window.
- hide
  `void hide()`

  Hides / minimizes the console window.

  Notes

  - In Safari (and possibly other browsers), hiding an `iframe` resets its document, thus destroying the console window.
- close
  `void close()`
  Removes the console window iframe from the main document.
- focus
  `void focus()`
  Brings the console window to the top and gives it the focus.
- focusCommandLine
  `void focusCommandLine()`
  Brings the console window to the top and gives the focus to the command line.
- focusSearch
  `void focusSearch()`
  Brings the console window to the top and gives the focus to the search box.
- evalCommandAndAppend
  `void evalCommandAndAppend(String expr)`
  Evaluates the expression and appends the result to the console.
- addCommandLineFunction
  `void addCommandLineFunction(String functionName, Function commandLineFunction)`

  Adds a function with the name specified to the list of functions available on the command line. This feature may be used to add custom functions to the command line.

  When you call the function on the command line, `commandLineFunction` is executed with the following three parameters:

  - appender. A reference to the appender in which the command was executed;
  - args. An array-like list of parameters passed into the function on the command line (actually a reference to an `arguments` object);
  - returnValue. This is an object with two properties that allow the function to control how the result is displayed:
    - appendResult. A boolean value that determines whether the returned value from this function is appended to the console. The default value is `true`;
    - isError. A boolean value that specifies whether the output of this function should be displayed as an error. The default value is `false`.

  The value returned by the function is formatted by the command layout and appended to the console.

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### BrowserConsoleAppender

Editions: Standardl

Writes log messages to the browser's built-in console, if present. This only works currently in Safari, Opera and Firefox with the excellent Firebug extension installed.

Notes

- As of log4javascript 1.3, the default threshold for this appender is `DEBUG` as opposed to `WARN` as it was previously;

- As of version 1.3, log4javascript has explicit support for Firebug's logging. This includes the following mapping of log4javascript's log levels onto Firebug's:

  - log4javascript `TRACE`, `DEBUG` -> Firebug `debug`
  - log4javascript `INFO` -> Firebug `info`
  - log4javascript `WARN` -> Firebug `warn`
  - log4javascript `ERROR`, `FATAL` -> Firebug `error`

  ... and the ability to pass objects into Firebug and take advantage of its object inspection. This is because the default layout is now `NullLayout`, which performs no formatting on an object.

#### Constructor

- BrowserConsoleAppender
  `BrowserConsoleAppender()`

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## Layouts

### Layout

There are a few methods common to all layouts:

#### Methods

- format
  `String format(LoggingEvent loggingEvent)`
  Parameters:
  - `loggingEvent`
  Formats the log message. You should override this method in your own layouts.
- ignoresThrowable
  `Boolean ignoresThrowable()`
  Returns whether the layout ignores an error object in a logging event passed to its `format` method.
- getContentType
  `String getContentType()`
  Returns the content type of the output of the layout.
- allowBatching
  `Boolean allowBatching()`
  Returns whether the layout's output is suitable for batching. `JsonLayout` and `XmlLayout` are the only built-in layouts that return true for this method.
- getDataValues
  `Array getDataValues(LoggingEvent loggingEvent)`
  Parameters:
  - `loggingEvent`
  Used internally by log4javascript in constructing formatted output for some layouts.
- setKeys
  `void setKeys(String loggerKey, String timeStampKey, String levelKey, String messageKey, String exceptionKey, String urlKey)`
  Parameters:
  - `loggerKey`
    Parameter to use for the log message's logger name. Default is `logger`.
  - `timeStampKey`
    Parameter to use for the log message's timestamp. Default is `timestamp`.
  - `levelKey`
    Parameter to use for the log message's level. Default is `level`.
  - `messageKey`
    Parameter to use for the message itself. Default is `message`.
  - `exceptionKey`
    Parameter to use for the log message's error (exception). Default is `exception`.
  - `urlKey`
    Parameter to use for the current page URL. Default is `url`.
  This method is used to change the default keys used to create formatted name-value pairs for the properties of a log message, for layouts that do this. These layouts are `JsonLayout` and `HttpPostDataLayout`.
- setCustomField
  `void setCustomField(String name, String value)`
  Parameters:
  - `name`
    Name of the custom property you wish to be included in the formmtted output.
  - `value`
    Value of the custom property you wish to be included in the formatted output.
  Some layouts (`JsonLayout`, `HttpPostDataLayout`, `PatternLayout` and `XmlLayout`) allow you to set custom fields (e.g. a session id to send to the server) to the formatted output. Use this method to set a custom field. If there is already a custom field with the specified name, its value will be updated with `value`.

  Notes

  - From version 1.4, the custom field value may be a function. In this case, the function is run at the time the layout's format method is called, with the following two parameters:

    - layout. A reference to the layout being used;
    - loggingEvent. A reference to the logging event being formatted.
- hasCustomFields
  `Boolean hasCustomFields()`
  Returns whether the layout has any custom fields.

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### NullLayout

Editions: All

The most basic layout. NullLayout's `format()` methods performs no formatting at all and simply returns the message logged.

#### Constructor

- NullLayout
  `NullLayout()`

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### SimpleLayout

Editions: Standard, Production

Provides basic formatting. SimpleLayout consists of the level of the log statement, followed by " - " and then the log message itself. For example,

`DEBUG - Hello world`

#### Constructor

- SimpleLayout
  `SimpleLayout()`

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### PatternLayout

Editions: All

Provides a flexible way of formatting a log message by means of a conversion pattern string. The behaviour of this layout is a full implementation of `PatternLayout` in log4j, with the exception of the set of conversion characters - log4javascript's is necessarily a subset of that of log4j with a few additions of its own, since many of the conversion characters in log4j only make sense in the context of Java.

The conversion pattern consists of literal text interspersed with special strings starting with a % symbol called conversion specifiers. A conversion specifier consists of the % symbol, a conversion character (possible characters are listed below) and format modifiers. For full documentation of the conversion pattern, see log4j's documentation. Below is a list of all conversion characters available in log4javascript.

#### Conversion characters

Conversion Character | Effect
--- | ---
a | Outputs log messages specified as an array. Behaves exactly like `%m`, except that multiple log messages are assumed to have been specified in the logging call as an array rather than as multiple parameters. Since: 1.4
c | Outputs the logger name.
d | Outputs the date of the logging event. The date conversion specifier may be followed by a date format specifier enclosed between braces. For example, `%d{HH:mm:ss,SSS}` or `%d{dd MMM yyyy HH:mm:ss,SSS}`. If no date format specifier is given then ISO8601 format is assumed. The date format specifier is the same as that used by Java's `SimpleDateFormat`. log4javascript includes a full implementation of SimpleDateFormat's `format` method, with the exception of the pattern letter 'z', (string representation of the timezone) for which the information is not available in JavaScript.
f | Outputs the value of a custom field set on the layout. If present, the specifier gives the index in the array of custom fields to use; otherwise, the first custom field in the array is used. Since: 1.3
m | Outputs the log messages of the logging event (i.e. the log messages supplied by the client code). As of version 1.4, multiple log messages may be supplied to logging calls. `%m` displays each log message (using the rules below) one after another, separated by spaces. As of version 1.3, an object may be specified as the log message and will be expanded to show its properties in the output, provided that a specifier containing the number of levels to expand is provided. If no specifier is provided then the message will be treated as a string regardless of its type. For example, `%m{1}` will display an expansion of the object one level deep, i.e. each property of the object will be displayed but if the property value is itself an object it will not be expanded and will appear as `[object Object]`.
n | Outputs a line separator.
p | Outputs the level of the logging event.
r | Outputs the number of milliseconds since log4javascript was initialized.
% | The sequence %% outputs a single percent sign.

#### Static properties

- TTCC_CONVERSION_PATTERN
  Built-in conversion pattern, equivalent to `%r %p %c - %m%n`.
- DEFAULT_CONVERSION_PATTERN
  Built-in conversion pattern, equivalent to `%m%n`.
- ISO8601_DATEFORMAT
  Built-in date format (and also the default), equivalent to `yyyy-MM-dd HH:mm:ss,SSS`.
- DATETIME_DATEFORMAT
  Built-in date format, equivalent to `dd MMM YYYY HH:mm:ss,SSS`.
- ABSOLUTETIME_DATEFORMAT
  Built-in date format, equivalent to `HH:mm:ss,SSS`.

#### Constructor

- PatternLayout
  `PatternLayout(String pattern)`
  Parameters:
  - `pattern`
    The conversion pattern string to use.

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### XmlLayout

Editions: Standard, Production

Based on log4j's `XmlLayout`, this layout formats a log message as a fragment of XML. An example of the format of the fragment is as follows:

    <log4javascript:event logger="[default]" timestamp="1201048234203" level="ERROR">
    <log4javascript:message><![CDATA[Big problem!]]></log4javascript:message>
    <log4javascript:exception><![CDATA[Nasty error on line number 1
        in file http://log4javascript.org/test.html]]></log4javascript:exception>
    </log4javascript:event>

Notes

- This layout supports batching of log messages when used in an `AjaxAppender`. A batch of messages is simply concatenated to form a string of several XML frgaments similar to that above.
- The `<log4javascript:exception>` element is only present if an exception was passed into the original log call.
- As of version 1.4, timestamps are returned as milliseconds since midnight of January 1, 1970 rather than seconds as in previous versions. This allows finer measurement of the time a logging event occurred and is also the JavaScript `Date` object's standard measurement.
- Also as of version 1.4, multiple messages may be specified as separate parameters in a single logging call. In `XmlLayout`, multiple messages may be formatted as a single combined message or may be formated as several `<log4javascript:message>` elements inside one `<log4javascript:messages>` element as shown below:

      <log4javascript:event logger="[default]" timestamp="1201048234203" level="ERROR">
      <log4javascript:messages>
          <log4javascript:message><![CDATA[Big problem!]]></log4javascript:message>
          <log4javascript:message><![CDATA[Value of x when this error
              occurred: 3]]></log4javascript:message>
      </log4javascript:messages>
      <log4javascript:exception><![CDATA[Nasty error on line number 1
          in file http://log4javascript.org/test.html]]></log4javascript:exception>
      </log4javascript:event>

- As of version 1.3, custom fields may be added to the output. Each field will add a tag of the following form inside the `<log4javascript:event>` tag:

      <log4javascript:customfield name="sessionid"><![CDATA[1234]]></log4javascript:customfield>

#### Constructor

- XmlLayout
  `XmlLayout([Boolean combineMessages])`
  - `combineMessages`
    Whether or not to format multiple log messages as a combined single `<log4javascript:message>` element composed of each individual message separated by line breaks or to include a `<log4javascript:message>` element for each message inside one `<log4javascript:messages>` element. If not specified, defaults to `true`.

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### JsonLayout

Editions: Standard, Production

Formats a logging event into JavaScript Object Notation (JSON). JSON is a subset of JavaScript's object literal syntax, meaning that log messages formatted with this layout can be interpreted directly by JavaScript and converted into objects. See json.org for more details about JSON.

Example:

    {
        "logger": "[default]",
        "timeStamp": 1201048234203,
        "level": "ERROR",
        "url": "http://log4javascript.org/test.html",
        "message": "Big problem!",
        "exception": "Nasty error on line number 1 in file
            http://log4javascript.org/test.html"
    }

The `exception` property is only present if an exception was passed into the original log call.

Notes

- This layout supports batching of log messages when used in an `AjaxAppender`. When sent singly the layout formats the log message as a single JavaScript object literal; when sent as a batch, the messages are formatted as an array literal whose elements are log message objects.

- As of version 1.3, custom fields may be added to the output. Each field will add a property of the following form to the main object literal:

          "sessionid": 1234

- From version 1.4, the variable names used for log event properties such as the message, timestamp and exception are specified using the `setKeys()` method of `Layout`.

- Also as of version 1.4, multiple messages may be specified as separate parameters in a single logging call. In `JsonLayout`, multiple messages may be formatted as a single combined message or may be formated as an array of messages as shown below:

      {
          "logger": "[default]",
          "timeStamp": 1201048234203,
          "level": "ERROR",
          "url": "http://log4javascript.org/test.html",
          "message": [
              "Big problem!",
              "Value of x when this error occurred: 3"
          ],
          "exception": "Nasty error on line number 1 in file
              http://log4javascript.org/test.html"
      }

#### Constructor

- JsonLayout
  `JsonLayout([Boolean readable, Boolean combineMessages])`
  Parameters:
  - `readable`
    Whether or not to format each log message with line breaks and tabs. If not specified, defaults to `false`.
  - `combineMessages`
    Whether or not to format multiple log messages as a combined single `message` property composed of each individual message separated by line breaks or to format multiple messages as an array. If not specified, defaults to `true`.

#### Methods

- isReadable
  `Boolean isReadable()`
  Returns whether or not to each log message is formatted with line breaks and tabs.

  Notes

  - `setReadable` has been removed in version 1.4. This property can be set via the constructor.

### HttpPostDataLayout

Editions: Standard, Production

Formats the log message as a simple URL-encoded string from which a simple server-side script may extract parameters such as the log message, severity and timestamp. This is the default layout for `AjaxAppender`.

#### Constructor

- HttpPostDataLayout
  `HttpPostDataLayout()`

Notes

- As of version 1.3, custom fields may be added to the output. Each field will be added as a parameter to the post data.
- From version 1.4, the variable names used for log event properties such as the message, timestamp and exception are specified using the `setKeys()` method of `Layout`.

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## Enabling / disabling log4javascript

All logging can be enabled or disabled in log4javascript in a number of ways:

- At any time, you can call `log4javascript.setEnabled(enabled)`. This will enable or disable all logging, depending on whether `enabled` is set to `true` or `false`.

- Assign a value to the global variable `log4javascript_disabled`. The idea of this is so that you can enable or disable logging for a whole site by including a JavaScript file in all your pages, and allowing this file to be included before log4javascript.js to guarantee that no logging can take place without having to alter log4javascript.js itself. Your included .js file would include a single line such as the following:

  `var log4javascript_disabled = true;`

- Assign your logger object a value of `log4javascript.getNullLogger()`.
- Replace your copy of log4javascript_x.js with stubs/log4javascript_x.js, provided in the distribution. This file has a stub version of each of the functions and methods in the log4javascript API and can simply be dropped in in place of the main file. The compressed version of the stub is typically 15 times smaller than the compressed version of the main file.

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## log4javascript error handling

log4javascript has a single rudimentary logger-like object of its own to handle messages generated by log4javascript itself. This logger is called `LogLog` and is accessed via `log4javascript.logLog`.

#### Methods

- setQuietMode
  `void setQuietMode(Boolean quietMode)`
  Parameters:
  - `quietMode`
    Whether to turn quiet mode on or off.
  Sets whether `LogLog` is in quiet mode or not. In quiet mode, no messages sent to `LogLog` have any visible effect. By default, quiet mode is switched off.
- setAlertAllErrors
  `void setAlertAllErrors(Boolean alertAllErrors)`
  Parameters:
  - `showAllErrors`
    Whether to show all errors or just the first.
  Sets how many errors `LogLog` will display alerts for. By default, only the first error encountered generates an alert to the user. If you turn all errors on by supplying `true` to this method then all errors will generate alerts.
- debug
  `void debug(String message[, Error exception])`
  Parameters:
  - `message`
  - `exception` [optional]
  Logs a debugging message to an in-memory list. This implementation is new in version 1.4.
- displayDebug
  `void displayDebug()`
  Displays an alert of all debugging messages. This method is new in version 1.4.
- warn
  `void warn(String message[, Error exception])`
  Parameters:
  - `message`
  - `exception` [optional]
  Currently has no effect.
- error
  `void error(String message[, Error exception])`
  Parameters:
  - `message`
  - `exception` [optional]
  Generates an alert to the user if and only if the error is the first one encountered and `setAlertAllErrors(true)` has not been called.

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## Differences between log4javascript and log4j

For the sake of keeping log4javascript as light and useful as possible, many of the features of log4j that seem over-complex or inappropriate for JavaScript have not been implemented. These include:

- Filters
- Configurators
- Renderers

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