Typesetting and Converting Mathematics
There are two main uses for MathJax:
Typesetting all the mathematics within a web page, and
Converting a string containing mathematics into another form.
In version 2, MathJax could perform the first function very well, but it was much harder to do the second. MathJax version 3 makes both easy to do. Both these tasks are described below.
Typesetting Math in a Web Page
MathJax makes it easy to typeset all the math in a web page, and in fact it will do this automatically when it is first loaded unless you configure it not to. So this is one of the easiest actions to perform in MathJax; if your page is static, there is nothing to do but load MathJax.
If your page is dynamic, and you may be adding math after the page is
loaded, then you will need to tell MathJax to typeset the mathematics
once it has been inserted into the page. There are two methods for
doing that: MathJax.typeset()
and
MathJax.typesetPromise()
.
The first of these, MathJax.typeset()
, typesets the page, and
does so immediately and synchronously, so when the call finishes, the
page will have been typeset. Note, however, that if the math includes
actions that require additional files to be loaded (e.g., TeX input
that uses require, or that includes autoloaded extensions), then
an error will be thrown. You can use the try/catch
command to
trap this condition.
The second, Mathjax.typesetPromise()
, performs the typesetting
asynchronously, and returns a promise that is resolved when the
typesetting is complete. This properly handles loading of external
files, so if you are expecting to process TeX input that can include
require or autoloaded extensions, you should use this form of
typesetting. It can be used with await
as part of a larger
async
function.
Both functions take an optional argument, which is an array of elements whose content should be processed. An element can be either an actual DOM element, or a CSS selector string for an element or collection of elements. Supplying an array of elements will restrict the typesetting to the contents of those elements only.
Handling Asynchronous Typesetting
It is generally a bad idea to try to perform multiple asynchronous
typesetting calls simultaneously, so if you are using
MathJax.typesetPromise()
to make several typeset calls, you
should chain them using the promises they return. For example:
MathJax.typesetPromise().then(() => {
// modify the DOM here
MathJax.typesetPromise();
}).catch((err) => console.log(err.message));
This approach can get complicated fast, however, so you may want to maintain a promise that can be used to chain the later typesetting calls. For example,
let promise = Promise.resolve(); // Used to hold chain of typesetting calls
function typeset(code) {
promise = promise.then(() => {code(); return MathJax.typesetPromise()})
.catch((err) => console.log('Typeset failed: ' + err.message));
return promise;
}
Then you can use typeset()
to run code that changes the DOM
and typesets the result. The code()
that you pass it does the
DOM modifications and returns the array of elements to typeset, or
null
to typeset the whole page. E.g.,
typeset(() => {
const math = document.querySelector('#math');
math.innerHTML = '$$\\frac{a}{1-a^2}$$';
return math;
});
would replace the contents of the element with id="math"
with the
specified fraction and have MathJax typeset it (asynchronously).
Because the then()
call returns the result of
MathJax.typesetPromise()
, which is itself a promise, the
then()
will not resolve until that promise is resolved; i.e.,
not until the typesetting is complete. Finally, since the
typeset()
function returns the promise
, you can use
await
in an async
function to wait for the typesetting to
complete:
await typeset(...);
Note that this doesn’t take the initial typesetting that MathJax
performs into account, so you might want to use
MathJax.startup.promise
in place of promise
above.
I.e., simply use
function typeset(code) {
MathJax.startup.promise = MathJax.startup.promise
.then(() => {code(); return MathJax.typesetPromise()})
.catch((err) => console.log('Typeset failed: ' + err.message));
return MathJax.startup.promise;
}
This avoids the need for the global promise
variable, and
makes sure that your typesetting doesn’t occur until the initial
typesetting is complete.
Resetting Automatic Equation Numbering
The TeX input jax allows you to automatically number equations. When modifying a page, this can lead to problems as numbered equations may be removed and added; most commonly, duplicate labels lead to issues.
You can reset equation numbering using the command
- MathJax.texReset([start])
where start
is the number at which to start equation numbering.
If you have inserted new content, that may require the entire page to be reprocessed in order to get the automatic numbering, labels, and references to be correct. In that case, you can do
MathJax.startup.document.state(0);
MathJax.texReset();
MathJax.typeset();
to force MathJax to reset the page to the state it was before MathJax processed it, reset the TeX automatic line numbering and labels, and then re-typeset the contents of the page from scratch.
Loading MathJax Only on Pages with Math
The MathJax combined configuration files are large, and so you may wish to include MathJax in your page only if it is necessary. If you are using a content-management system that puts headers and footers into your pages automatically, you may not want to include MathJax directly, unless most of your pages include math, as that would load MathJax on all your pages. Once MathJax has been loaded, it should be in the browser’s cache and load quickly on subsequent pages, but the first page a reader looks at will load more slowly. In order to avoid that, you can use a script like the following one that checks to see if the content of the page seems to include math, and only loads MathJax if it does. Note that this is not a very sophisticated test, and it may think there is math in some cases when there really isn’t but it should reduce the number of pages on which MathJax will have to be loaded.
Create a file called check-for-tex.js
containing the following:
(function () {
var body = document.body.textContent;
if (body.match(/(?:\$|\\\(|\\\[|\\begin\{.*?})/)) {
if (!window.MathJax) {
window.MathJax = {
tex: {
inlineMath: {'[+]': [['$', '$']]}
}
};
}
var script = document.createElement('script');
script.src = 'https://cdn.jsdelivr.net/npm/mathjax@3/es5/tex-chtml.js';
document.head.appendChild(script);
}
})();
and then use
<script src="check-for-tex.js" defer></script>
in order to load the script when the page content is ready. Note
that you will want to include the path to the location where you
stored check-mathjax.js
, that you should change
tex-chtml.js
to whatever component file you want to use, and that
the window.MathJax
value should be set to whatever configuration
you want to use. In this case, it just adds dollar signs to the
in-line math delimiters. Finally, adjust the body.match()
regular
expression to match whatever you are using for math delimiters.
This simply checks if there is something that looks like a TeX in-line or displayed math delimiter, and loads MathJax if there is. If you are using different delimiters, you will need to change the pattern to include those (and exclude any that you don’t use). If you are using AsciiMath instead of TeX, then change the pattern to look for the AsciiMath delimiters.
If you are using MathML, you may want to use
if (document.body.querySelector('math')) {...}
for the test instead (provided you aren’t using namespace prefixes, like <m:math>).
Converting a Math String to Other Formats
An important use case for MathJax is to convert a string containing mathematics (in one of the three forms that MathJax understands) and convert it into another form (either MathML, or one of the output formats that MathJax supports). This was difficult to do in MathJax version 2, but easy to do in version 3.
When MathJax starts up, it creates methods for converting from the
input format(s) to the output format(s) that you have loaded, and to
MathML format. For example, if you have loaded the MathML input jax
and the SVG output jax (say by using the mml-svg
component), then
MathJax will create the following conversion methods for you:
- MathJax.mathml2svg(math[,options])
- MathJax.mathml2svgPromise(math[,options])
- MathJax.mathml2mml(math[,options])
- MathJax.mathml2mmlPromise(math[,options])
If you had loaded the TeX input jax as well, you would also get four
more methods, with tex
in place of mathml
.
As the names imply, the Promise
functions perform the conversion
asynchronously, and return promises, while the others operate
synchronously and return the converted form immediately. The first
two functions (and any others like them) produce DOM elements as the
results of the conversion, with the promise versions passing that to
their then()
functions as their argument (see the section on
Asynchronous Conversion below), and the non-promise versions returning
them directly. You can insert these DOM elements into the document
directly, or you can use their outerHTML
property to obtain
their serialized string form.
The functions that convert to MathML produce serialized MathML strings
automatically, rather than DOM elements. (You can use the browser’s
DOMParser
object to convert the string into a MathML DOM tree
if you need one.)
Conversion Options
All four of these functions require an argument that is the math
string to be converted (e.g., the serialized MathML string, or in the
case of tex2chtml()
, the TeX or LaTeX string). You can also
pass a second argument that is an object containing options that
control the conversion process. The options that can be included are:
display
, a boolean specifying whether the math is in display-mode or not (for TeX input). Default istrue
.em
, a number giving the number of pixels in anem
for the surrounding font. Default is16
.ex
, a number giving the number of pixels in anex
for the surrounding font. Default is8
.containerWidth
, a number giving the width of the container, in pixels. Default is 80 times theex
value.lineWidth'
, a number giving the line-breaking width inem
units. Default is a very large number (100000), so effectively no line breaking.scale
, a number giving a scaling factor to apply to the resulting conversion. Default is 1.
For example,
let html = MathJax.tex2chtml('\\sqrt{x^2+1}', {em: 12, ex: 6, display: false});
would convert the TeX expression \sqrt{x^2+1}
to HTML as an
in-line expression, with em
size being 12 pixels and ex
size
being 6 pixels. The result will be a DOM element containing the HTML
for the expression. Similarly,
let html = MathJax.tex2chtml('\\sqrt{x^2+1}', {em: 12, ex: 6, display: false});
let text = html.outerHTML;
sets text
to be the serialized HTML string for the expression.
Obtaining the Output Metrics
Since the em
, ex
, and containerWidth
all
depend on the location where the math will be placed in the document
(they are values based on the surrounding text font and the container
elements width), MathJax provides a method for obtaining these values
from a given DOM element. The method
- MathJax.getMetricsFor(node, display)
takes a DOM element (node
) and a boolean (display
), indicating
if the math is in display mode or not, and returns an object
containing all six of the options listed above. You can pass this
object directly to the conversion methods discussed above. So you can
do something like
let node = document.querySelector('#math');
let options = MathJax.getMetricsFor(node, true);
let html = MathJax.tex2svg('\\sqrt{x^2+1}', options);
node.appendChild(html);
in order to get get the correct metrics for the (eventual) location of
the math that is being converted. Of course, it would be easier to
simply insert the TeX code into the page and use
MathJax.typeset()
to typeset it, but this is just an example
to show you how to obtain the metrics from a particular location in
the page.
Note that obtaining the metrics causes a page refresh, so it is expensive to do this. If you need to get the metrics from many different locations, there are more efficient ways, but these are advanced topics to be dealt with elsewhere.
Obtaining the Output Stylesheet
The output from the SVG and CommonHTML output jax both depend on CSS stylesheets in order to properly format their results. You can obtain the SVG stylesheet element by calling
MathJax.svgStylesheet();
and the HTML stylesheet from
MathJax.chtmlStylesheet();
The CommonHTML output jax CSS can be quite large, so the output jax tries to minimize the stylesheet by including only the styles that are actually needed for the mathematics that has been processed by the output jax. That means you should request the stylesheet only after you have typeset the mathematics itself.
Moreover, if you typeset several expressions, the stylesheet will include everything needed for all the expressions you have typeset. If you want to reset the stylesheet, then use
MathJax.startup.output.clearCache();
if the output jax is the CommonHTML output jax. So if you want to
produce the style sheet for a single expression, issue the
clearCache()
command just before the tex2chtml()
call.
Asynchronous Conversion
If you are converting TeX or LaTeX that might use require to load extensions, or where extensions might be autoloaded, you will either need to use one of the “full” components that include all the extensions, or preload all the extensions you need if you plan to use the synchronous calls listed above. Otherwise, you can use the promise-based calls, which handle the loading of extensions transparently.
For example,
let node = document.querySelector('#math');
let options = MathJax.getMetricsFor(node, true);
MathJax.tex2chtmlPromise('\\require{bbox}\\bbox[red]{\\sqrt{x^2+1}}', options)
.then((html) => {
node.appendChild(html);
let sheet = document.querySelector('#MJX-CHTML-styles');
if (sheet) sheet.parentNode.removeChild(sheet);
document.head.appendChild(MathJax.chtmlStylesheet());
});
would get the metrics for the element with id="math"
, convert
the TeX expression using those metrics (properly handling the
asynchronous load needed for the \require
command); then when the
expression is typeset, it is added to the document and the CHTML
stylesheet is updated.