MathJax is designed to be included via a <script> tag in the <head> section of your HTML document, and it does rely on being part of the original document in that it uses an onload or DOMContentLoaded event handler to synchronize its actions with the loading of the page. If you wish to insert MathJax into a document after it has been loaded, that will normally occur after the page’s onload handler has fired, and prior to version 2.0, MathJax had to be told not to wait for the page onload event by calling MathJax.Hub.Startup.onload() by hand. That is no longer necessary, as MathJax v2.0 detects whether the page is already available and when it is, it processes it immediately rather than waiting for an event that has already happened.

Here is an example of how to load and configure MathJax dynamically:

(function () {
var script = document.createElement("script");
script.type = "text/javascript";
script.src  = "https://example.com/MathJax.js?config=TeX-AMS-MML_HTMLorMML";
})();


If you need to provide in-line configuration, you can do that using a MathJax’s configuration script:

(function () {
script = document.createElement("script");
script.type = "text/x-mathjax-config";
script[(window.opera ? "innerHTML" : "text")] =
"MathJax.Hub.Config({\n" +
"  tex2jax: { inlineMath: [['$','$'], ['\\$','\\$']] }\n" +
"});"
script = document.createElement("script");
script.type = "text/javascript";
script.src  = "https://example.com/MathJax.js?config=TeX-AMS-MML_HTMLorMML";
})();


You can adjust the configuration to your needs, but be careful to get the commas right, as Internet Explorer 6 and 7 will not tolerate an extra comma before a closing brace. The window.opera test is because some versions of Opera don’t handle setting script.text properly, while some versions of Internet Explorer don’t handle setting script.innerHTML.

Note that the only reliable way to configure MathJax is to use an in-line configuration block of the type discussed above. You should not call MathJax.Hub.Config() directly in your code, as it will not run at the correct time — it will either run too soon, in which case MathJax may not be defined and the function will throw an error, or it will run too late, after MathJax has already finished its configuration process, so your changes will not have the desired effect.

## MathJax and GreaseMonkey¶

You can use techniques like the ones discussed above to good effect in GreaseMonkey scripts. There are GreaseMonkey work-alikes for all the major browsers:

Note, however, that most browsers don’t allow you to insert a script that loads a file:// URL into a page that comes from the web (for security reasons). That means that you can’t have your GreaseMonkey script load a local copy of MathJax, so you have to refer to a server-based copy. The MathJax CDN works nicely for this.

Here is a script that runs MathJax in any document that contains MathML (whether it includes MathJax or not). That allows browsers that don’t have native MathML support to view any web pages with MathML, even if they say it only works in Firefox and IE+MathPlayer.

// ==UserScript==
// @name           MathJax MathML
// @namespace      http://www.mathjax.org/
// @description    Insert MathJax into pages containing MathML
// @include        *
// ==/UserScript==

if ((window.unsafeWindow == null ? window : unsafeWindow).MathJax == null) {
if ((document.getElementsByTagName("math").length > 0) ||
(document.getElementsByTagNameNS == null ? false :
(document.getElementsByTagNameNS("http://www.w3.org/1998/Math/MathML","math").length > 0))) {
var script = document.createElement("script");
script.type = "text/javascript";
script.src = "https://example.com/MathJax.js?config=TeX-AMS-MML_HTMLorMML-full";
}
}


Source: mathjax_mathml.user.js

Here is a script that runs MathJax in Wikipedia pages after first converting the math images to their original TeX code.

// ==UserScript==
// @name           MathJax in Wikipedia
// @namespace      http://www.mathjax.org/
// @include        http://en.wikipedia.org/wiki/*
// ==/UserScript==

if ((window.unsafeWindow == null ? window : unsafeWindow).MathJax == null) {
//
//  Replace the images with MathJax scripts of type math/tex
//
var images = document.getElementsByTagName('img'), count = 0;
for (var i = images.length - 1; i >= 0; i--) {
var img = images[i];
if (img.className === "tex") {
var script = document.createElement("script"); script.type = "math/tex";
if (window.opera) {script.innerHTML = img.alt} else {script.text = img.alt}
img.parentNode.replaceChild(script,img); count++;
}
}
if (count) {
//
//  Load MathJax and have it process the page
//
var script = document.createElement("script");
script.type = "text/javascript";
script.src = "https://example.com/MathJax.js?config=TeX-AMS-MML_HTMLorMML-full";