.. _startup-sequence:

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The MathJax Startup Sequence
****************************

When you load ``MathJax.js`` into a web page, it configures itself and
immediately begins loading the components it needs.  As MathJax starts
up, it uses its :ref:`signaling mechanism <synchronization>`
to indicate the actions that it is taking so that MathJax extensions
can tie into the initialization process, and so other applications
within the page can synchronize their actions with MathJax.  

The startup process performs the following actions:

- It creates the ``MathJax`` variable, and defines the following
  subsystems: 

  - ``MathJax.Object`` (object-oriented programming model)
  - ``MathJax.Callback`` (callbacks, signals, and queues)
  - ``MathJax.Ajax`` (file-loading and style-creation code)
  - ``MathJax.HTML`` (support code for creating HTML elements)
  - ``MathJax.Message`` (manages the menu line in the lower left)
  - ``MathJax.Hub`` (the core MathJax functions)

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- It then creates the base ``MathJax.InputJax``,
  ``MathJax.OutputJax``, and ``MathJax.ElementJax`` objects.

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- MathJax sets up the default configuration, and creates the
  signal objects used for the startup and hub actions.

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- MathJax locates the ``<script>`` tag that loaded the ``MathJax.js``
  file, and sets the ``MathJax.Hub.config.root`` value to reflect the
  location of the MathJax root directory.

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- MathJax determines the browser being used and its version.  It sets
  up the ``MathJax.Hub.Browser`` object, which includes the browser
  name and version, plus ``isMac``, ``isPC``, ``isMSIE``, and so on.

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- MathJax set up the ``MathJax.Hub.queue`` command queue, and
  populates it with the commands MathJax runs at startup.  This
  includes creating the ``MathJax.Hub.Startup.onload`` onload
  handler that is used to synchronize MathJax's action with the
  loading of the page.

Once the ``MathJax.Hub.queue`` is created, the following actions are
pushed into the queue:

1.  Post the ``Begin`` startup signal

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2.  Perform the configuration actions:

    - Post the ``Begin Config`` startup signal
    - Execute the content of the ``<script>`` that loaded MathJax,
      or load the ``config/MathJax.js`` file if the ``<script>``
      is empty
    - If the ``MathJax.Hub.config.delayStartupUntil`` value is set,
      wait until its condition is met
    - load the files listed in the ``MathJax.Hub.config.config`` array
    - Post the ``End Config`` startup signal

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3.  Load the cookie values:

    - Post the ``Begin Cookie`` startup signal
    - Load the menu cookie values
    - Use the cookie to set the renderer, if it is set
    - Post the ``End Cookie`` startup signal

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4.  Define the MathJax styles:

    - Post the ``Begin Styles`` startup signal
    - Load the stylesheet files from the ``MathJax.Hub.config.stylesheets`` array
    - Define the stylesheet described in ``MathJax.Hub.config.styles``
    - Post the ``End Styles`` startup signal

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5.  Load the jax configuration files:

    - Post the ``Begin Jax`` startup signal
    - Load the jax config files from the ``MathJax.Hub.config.jax`` array

      - The jax will register themselves when they are loaded

    - Post the ``End Jax`` startup signal

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6.  Load the extension files:

    - Post the ``Begin Extension`` startup signal
    - Load the files from the ``MathJax.Hub.config.extensions`` array

      - Most extensions will post a ``Extension [name] Ready``
        startup message when they are loaded (where ``[name]`` is
        the name of the extension)

    - Post the ``End Extension`` startup signal

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7.  Wait for the onload handler to fire

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8.  Set ``MathJax.isReady`` to ``true``

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9.  Perform the typesetting pass (preprocessors and processors)

    - Post the ``Begin Typeset`` startup signal
    - Post the ``Begin PreProcess`` hub signal
    - Run the registered preprocessors
    - Post the ``End PreProcess`` hub signal
    - Clear the hub signal history
    - Post the ``Begin Process`` hub signal
    - Process the math script elements on the page

      - Each new math element generates a ``New Math`` hub signal
        with the math element's ID

    - Post the ``End Process`` hub signal
    - Post the ``End Typeset`` startup signal

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10. Post the ``End`` startup signal