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# The MathJax.Hub Object

The MathJax Hub, MathJax.Hub, is the main control structure for MathJax. It is where input and output jax are tied together, and it is what handles processing of the MathJax `<script>` tags. Processing of the mathematics on the page may require external files to be loaded (when the mathematics includes less common functionality, for example, that is defined in an extension file), and since file loading is asynchronous, a number of the methods below may return before their actions are completed. For this reason, they include callback functions that are called when the action completes. These can be used to synchronize actions that require the mathematics to be completed before those action occur. See the Using Callbacks documentation for more details.

## Properties

`config: { ... }`

  This holds the configuration parameters for MathJax. Set these values using `MathJax.Hub.Config()` described below. The options and their default values are given in the Core Options reference page.

`processUpdateTime: 500`

  The minimum time (in milliseconds) between updates of the “Processing Math” message.

`signal`

  The hub processing signal (tied to the `MathJax.Hub.Register.MessageHook()` method).

`Browser`

  The name of the browser as determined by MathJax. It will be one of `Firefox`, `Safari`, `Chrome`, `Opera`, `MSIE`, `Konqueror`, or `unkown`. This is actually an object with additional properties and methods concerning the browser:

  `version`

    The browser version number, e.g., `"4.0"`

  `isMac and isPC`

    These are boolean values that indicate whether the browser is running on a Macintosh computer or a Windows computer. They will both be `false` for a Linux computer

  `isForefox, isSafari, isChrome, isOpera, isMSIE, isKonqueror`

    These are `true` when the browser is the indicated one, and `false` otherwise.

  `versionAtLeast(version)`

    This tests whether the browser version is at least that given in the version string. Note that you can not simply do a numeric comparison, as version 4.10 should be considered later than 4.9, for example. Similarly, 4.10 is different from 4.1, for instance.

  `Select(choices)`

    This lets you perform browser-specific functions. Here, choices is an object whose properties are the names of the browsers and whose values are the functions to be performed. Each function is passed one parameter, which is the `MathJax.Hub.Browser` object. You do not need to include every browser as one of your choices (only those for which you need to do special processing. For example:

        MathJax.Hub.Browser.Select(
          MSIE: function (browser) {
            if (browser.versionAtLeast("8.0")) {... do version 8 stuff ... }
            ... do general MSIE stuff ...
          },

          Firefox: function (browser) {
            if (browser.isMac) {... do Mac stuff ... }
            ... do general Firefox stuff
          }
        );

## Methods

`Config`(options)

  Sets the configuration options (stored in `MathJax.Hub.config`) to the values stored in the options object. See Configuring MathJax for details on how this is used and the options that you can set.

  Parameters : | options — object containing options to be set
  Returns : | `null`

`Register.PreProcessor(callback)`

  Used by preprocessors to register themselves with MathJax so that they will be called during the `MathJax.Hub.PreProcess()` action.

  Parameters : | callback — the callback specification for the preprocessor
  Returns : | `null`

`Register.MessageHook(type,callback)`

  Registers a listener for a particular message being sent to the hub processing signal (where PreProcessing, Processing, and New Math messages are sent). When the message equals the type, the callback will be called with the message as its parameter.

  Parameters : | type — a string indicating the message to look for callback — a callback specification
  Returns : | `null`

`Register.StartupHook(type,callback)`

  Registers a listener for a particular message being sent to the startup signal (where initialization and component startup messages are sent). When the message equals the type, the callback will be called with the message as its parameter. See the :ref:`Using Signals <using-signals> dcocumentation for more details.

  Parameters : | type — a string indicating the message to look for callback — a callback specification
  Returns : | `null`

`Register.LoadHook(file,callback)`

  Registers a callback to be called when a particular file is completely loaded and processed. (The callback is called when the file makes its `MathJax.Ajax.loadComplete()` call.) The file should be the complete file name, e.g., `"[MathJax]/config/MathJax.js"`.

  Parameters : | file — the name of the file to wait for callback — a callback specification
  Returns : | the callback object

`Queue`(callback, ...)

  Pushes the given callbacks onto the main MathJax command queue. This synchronizes the commands with MathJax so that they will be performed in the proper order even when some run asynchronously. See Using Queues for more details about how to use queues, and the MathJax queue in particular. You may supply as many callback specifications in one call to the `Queue()` method as you wish.

  Parameters : | callback — a callback specification
  Returns : | the callback object for the last callback added to the queue

`Typeset`([element[, callback]])

  Calls the preprocessors on the given element, and then typesets any math elements within the element. If no element is provided, the whole document is processed. The element is either the DOM id of the element, or a reference to the DOM element itself. The callback is called when the process is complete. See the Modifying Math section for details of how to use this method properly.

  Parameters : | element — the element whose math is to be typeset callback — the callback specification
  Returns : | the callback object

`PreProcess`([element[, callback]])

  Calls the loaded preprocessors on the entire document, or on the given DOM element. The element is either the DOM id of the element, or a reference to the DOM element itself. The callback is called when the processing is complete.

  Parameters : | element — the element to be preprocessed callback — the callback specification
  Returns : | the callback object

`Process`([element[, callback]])

  Scans either the entire document or a given DOM element for MathJax `<script>` tags and processes the math those tags contain. The element is either the DOM id of the element to scan, or a reference to the DOM element itself. The callback is called when the processing is complete.

  Parameters : | element — the element to be processed callback — the callback specification
  Returns : | the callback object

`Update`([element[, callback]])

  Scans either the entire document or a given DOM element for mathematics that has changed since the last time it was processed, or is new, and typesets the mathematics they contain. The element is either the DOM id of the element to scan, or a reference to the DOM element itself. The callback is called when the processing is complete.

  Parameters : | element — the element to be updated callback — the callback specification
  Returns : | the callback object

`Reprocess`([element[, callback]])

  Removes any typeset mathematics from the document or DOM element, and then processes the mathematics again, re-typesetting everything. This may be necessary, for example, if the CSS styles have changed and those changes would affect the mathematics. The element is either the DOM id of the element to scan, or a reference to the DOM element itself. The callback is called when the processing is complete.

  Parameters : | element — the element to be reprocessed callback — the callback specification
  Returns : | the callback object

`getAllJax`([element])

  Returns a list of all the element jax in the document or a specific DOM element. The element is either the DOM id of the element, or a reference to the DOM element itself.

  Parameters : | element — the element to be searched
  Returns : | array of element jax objects

`getJaxByType`(type[, element])

  Returns a list of all the element jax of a given MIME-type in the document or a specific DOM element. The element is either the DOM id of the element to search, or a reference to the DOM element itself.

  Parameters : | type — MIME-type of element jax to find element — the element to be searched
  Returns : | array of element jax objects

`getJaxByInputType`(type[, element])

  Returns a list of all the element jax associated with input `<script>` tags with the given MIME-type within the given DOM element or the whole document. The element is either the DOM id of the element to search, or a reference to the DOM element itself.

  Parameters : | type — MIME-type of input (e.g., `"math/tex"`) element — the element to be searched
  Returns : | array of element jax objects

`getJaxFor`(element)

  Returns the element jax associated with a given DOM element. If the element does not have an associated element jax, `null` is returned. The element is either the DOM id of the element, or a reference to the DOM element itself.

  Parameters : | element — the element whose element jax is required
  Returns : | element jax object or `null`

`isJax`(element)

  Returns `0` if the element is not a `<script>` that can be processed by MathJax or the result of an output jax, returns `-1` if element is an unprocessed `<script>` tag that could be handled by MathJax, and returns `1` if element is a processed `<script>` tag or an element that is the result of an output jax.

  Parameters : | element — the element to inspect
  Returns : | integer (-1, 0, 1)

`Insert`(dst, src)

  Inserts data from the src object into the dst object. The key:value pairs in src are (recursively) copied into dst, so that if value is itself an object, its contents is copied into the corresponding object in dst. That is, objects within src are merged into the corresponding objects in dst (they don’t replace them).

  Parameters : | dst — the destination object src — the source object
  Returns : | the modified destination object

`formatError`(script, error)

  This is called when an internal error occurs during the processing of a math element (i.e., an error in the MathJax code itself). The script is a reference to the `<script>` tag where the error occurred, and error is the `Error` object for the error. The default action is to insert an HTML snippet at the location of the script, but this routine can be overriden durring MathJax configuration in order to perform some other action. `MathJax.Hub.lastError` holds the `error` value of the last error on the page.

  Parameters : | script — the `<script>` tag causing the error error — the `Error` object for the error
  Returns : | `null`

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