Question

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 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)

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

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

• 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.

• 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.

• 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

2. Perform the configuration actions:
   • Post the Begin Config startup signal
   • Load any configuration files specified via config= as a script parameter
   • Execute the content of the <script> that loaded MathJax, if it is not empty
   • Wait for the delayStartupUntil condition to be met, if one was specified
   • Execute any text/x-mathjax-config script blocks
   • load the files listed in the MathJax.Hub.config.config array
   • Post the End Config startup signal

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

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

5. Initialize the Message system (the grey information box in the lower left)

6. 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

7. Load the extension files:
   • Post the Begin Extensions startup signal
   • Load the files from the MathJax.Hub.config.extensions array
     • Most extensions will post a [name] Ready or Extension [name] Ready startup message when they are loaded (where [name] is the name of the extension)
   • Post the End Extensions startup signal

8. Set the MathJax menu’s renderer value based on the jax that have been loaded

9. Wait for the onload handler to fire (in MathJax v2.0 this can occur on the DOMContentLoaded event rather than the page’s onload event, so processing of mathematics can start earlier)

10. Set MathJax.isReady to true

11. 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
      • There are a number of Hub signals generated during math processing, including a signal that a Math action is starting (with a parameter indicating what action that is), Begin and End Math Input messages, and Begin and End Math Output signals.
      • 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

12. Jump to the location specified in the URL’s hash reference, if any.

13. Initiate timers to load the zoom and menu code, if it hasn’t already been loading in the configuration (so it will be ready when the user needs it).

14. Post the End startup signal

The loading of the jax and extensions in steps 5 and 6 are now done in parallel, rather than sequentially. That is, all the jax and extensions are requested simultaneously, so they load concurrently. That means they can load in any order, and that the begin and end signals for the jax and extensions can be intermixed. (In general, you will get Begin Jax followed by Begin Extensions, but the order of End Jax and End Extensions will depend on the files being loaded.) Both 5 and 6 must complete, however, before 7 will be performed.

See the test/sample-signals.html file to see the signals in action.