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KaTeX

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KaTeX is a fast, easy-to-use JavaScript library for TeX math rendering on the web.

  • Fast: KaTeX renders its math synchronously and doesn't need to reflow the page. See how it compares to a competitor in this speed test.
  • Print quality: KaTeX’s layout is based on Donald Knuth’s TeX, the gold standard for math typesetting.
  • Self contained: KaTeX has no dependencies and can easily be bundled with your website resources.
  • Server side rendering: KaTeX produces the same output regardless of browser or environment, so you can pre-render expressions using Node.js and send them as plain HTML.

KaTeX supports all major browsers, including Chrome, Safari, Firefox, Opera, Edge, and IE 9 - IE 11. More information can be found on the list of supported commands and on the wiki.

Usage

You can download KaTeX and host it on your server or include the katex.min.js and katex.min.css files on your page directly from a CDN:

<link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/katex@0.10.0-beta/dist/katex.min.css" integrity="sha384-9tPv11A+glH/on/wEu99NVwDPwkMQESOocs/ZGXPoIiLE8MU/qkqUcZ3zzL+6DuH" crossorigin="anonymous">
<script src="https://cdn.jsdelivr.net/npm/katex@0.10.0-beta/dist/katex.min.js" integrity="sha384-U8Vrjwb8fuHMt6ewaCy8uqeUXv4oitYACKdB0VziCerzt011iQ/0TqlSlv8MReCm" crossorigin="anonymous"></script>

In-browser rendering

Call katex.render with a TeX expression and a DOM element to render into:

katex.render("c = \\pm\\sqrt{a^2 + b^2}", element);

To avoid escaping the backslash (double backslash), you can use String.raw (but beware that ${, \u and \x may still need escaping):

katex.render(String.raw`c = \pm\sqrt{a^2 + b^2}`, element);

If KaTeX can't parse the expression, it throws a katex.ParseError error.

Server side rendering or rendering to a string

To generate HTML on the server or to generate an HTML string of the rendered math, you can use katex.renderToString:

var html = katex.renderToString("c = \\pm\\sqrt{a^2 + b^2}");
// '<span class="katex">...</span>'

Make sure to include the CSS and font files, but there is no need to include the JavaScript. Like render, renderToString throws if it can't parse the expression.

Security

Any HTML generated by KaTeX should be safe from <script> or other code injection attacks. (See maxSize below for preventing large width/height visual affronts, see maxExpand below for preventing infinite macro loop attacks, and see allowedProtocols below for preventing certain protocols in \href) Of course, it is always a good idea to sanitize the HTML, though you will need a rather generous whitelist (including some of SVG and MathML) to support all of KaTeX.

Handling errors

If KaTeX encounters an error (invalid or unsupported LaTeX) and throwOnError hasn't been set to false, then it will throw an exception of type katex.ParseError. The message in this error includes some of the LaTeX source code, so needs to be escaped if you want to render it to HTML. In particular, you should convert &, <, > characters to &amp;, &lt;, &gt; (e.g., using _.escape) before including either LaTeX source code or exception messages in your HTML/DOM. (Failure to escape in this way makes a <script> injection attack possible if your LaTeX source is untrusted.) Alternatively, you can set throwOnError to false to use built-in behavior of rendering the LaTeX source code with hover text stating the error.

Rendering options

You can provide an object of options as the last argument to katex.render and katex.renderToString. Available options are:

  • displayMode: boolean. If true the math will be rendered in display mode, which will put the math in display style (so \int and \sum are large, for example), and will center the math on the page on its own line. If false the math will be rendered in inline mode. (default: false)
  • throwOnError: boolean. If true (the default), KaTeX will throw a ParseError when it encounters an unsupported command or invalid LaTeX. If false, KaTeX will render unsupported commands as text, and render invalid LaTeX as its source code with hover text giving the error, in the color given by errorColor.
  • errorColor: string. A color string given in the format "#XXX" or "#XXXXXX". This option determines the color that unsupported commands and invalid LaTeX are rendered in when throwOnError is set to false. (default: #cc0000)
  • macros: object. A collection of custom macros. Each macro is a property with a name like \name (written "\\name" in JavaScript) which maps to a string that describes the expansion of the macro. Single-character keys can also be included in which case the character will be redefined as the given macro (similar to TeX active characters). This object will be modified if the LaTeX code defines its own macros via \gdef, which enables consecutive calls to KaTeX to share state.
  • colorIsTextColor: boolean. If true, \color will work like LaTeX's \textcolor, and take two arguments (e.g., \color{blue}{hello}), which restores the old behavior of KaTeX (pre-0.8.0). If false (the default), \color will work like LaTeX's \color, and take one argument (e.g., \color{blue}hello). In both cases, \textcolor works as in LaTeX (e.g., \textcolor{blue}{hello}).
  • maxSize: number. All user-specified sizes, e.g. in \rule{500em}{500em}, will be capped to maxSize ems. If set to Infinity (the default), users can make elements and spaces arbitrarily large.
  • maxExpand: number. Limit the number of macro expansions to the specified number, to prevent e.g. infinite macro loops. If set to Infinity, the macro expander will try to fully expand as in LaTeX. (default: 1000)
  • allowedProtocols: string[]. Allowed protocols in \href. Use _relative to allow relative urls, and * to allow all protocols. (default: ["http", "https", "mailto", "_relative"])
  • strict: boolean or string or function (default: "warn"). If false or "ignore", allow features that make writing LaTeX convenient but are not actually supported by (Xe)LaTeX (similar to MathJax). If true or "error" (LaTeX faithfulness mode), throw an error for any such transgressions. If "warn" (the default), warn about such behavior via console.warn. Provide a custom function handler(errorCode, errorMsg, token) to customize behavior depending on the type of transgression (summarized by the string code errorCode and detailed in errorMsg); this function can also return "ignore", "error", or "warn" to use a built-in behavior. A list of such features and their errorCodes:
    • "unknownSymbol": Use of unknown Unicode symbol, which will likely also lead to warnings about missing character metrics, and layouts may be incorrect (especially in terms of vertical heights).
    • "unicodeTextInMathMode": Use of Unicode text characters in math mode.
    • "mathVsTextUnits": Mismatch of math vs. text commands and units/mode. A second category of errorCodes never throw errors, but their strictness affects the behavior of KaTeX:
    • "newLineInDisplayMode": Use of \\ or \newline in display mode (outside an array/tabular environment). In strict mode, no line break results, as in LaTeX.

For example:

katex.render("c = \\pm\\sqrt{a^2 + b^2}\\in\\RR", element, {
  displayMode: true,
  macros: {
    "\\RR": "\\mathbb{R}"
  }
});

Automatic rendering of math on a page

Math on the page can be automatically rendered using the auto-render extension. See the Auto-render README for more information.

Font size and lengths

By default, KaTeX math is rendered in a 1.21× larger font than the surrounding context, which makes super- and subscripts easier to read. You can control this using CSS, for example:

.katex { font-size: 1.1em; }

KaTeX supports all TeX units, including absolute units like cm and in. Absolute units are currently scaled relative to the default TeX font size of 10pt, so that \kern1cm produces the same results as \kern2.845275em. As a result, relative and absolute units are both uniformly scaled relative to LaTeX with a 10pt font; for example, the rectangle \rule{1cm}{1em} has the same aspect ratio in KaTeX as in LaTeX. However, because most browsers default to a larger font size, this typically means that a 1cm kern in KaTeX will appear larger than 1cm in browser units.

Common Issues

  • Many Markdown preprocessors, such as the one that Jekyll and GitHub Pages use, have a "smart quotes" feature. This changes ' to which is an issue for math containing primes, e.g. f'. This can be worked around by defining a single character macro which changes them back, e.g. {"’", "'"}.
  • KaTeX follows LaTeX's rendering of aligned and matrix environments unlike MathJax. When displaying fractions one above another in these vertical layouts there may not be enough space between rows for people who are used to MathJax's rendering. The distance between rows can be adjusted by using \\[0.1em] instead of the standard line separator distance.
  • KaTeX does not support the align environment because LaTeX doesn't support align in math mode. The aligned environment offers the same functionality but in math mode, so use that instead or define a macro that maps align to aligned.
  • MathJax defines \color to be like \textcolor by default; set KaTeX's colorIsTextColor option to true for this behavior. KaTeX's default behavior matches MathJax with its color.js extension enabled.

Libraries

Angular2+

  • ng-katex Angular module to write beautiful math expressions with TeX syntax boosted by KaTeX library

React

  • react-latex React component to render latex strings, based on KaTeX
  • react-katex React components that use KaTeX to typeset math expressions

Ruby

  • katex-ruby Provides server-side rendering and integration with popular Ruby web frameworks (Rails, Hanami, and anything that uses Sprockets).

AsciiMath

If you want to render math written in AsciiMath, you'll need to first convert AsciiMath into LaTeX input, then call KaTeX.

Contributing

See CONTRIBUTING.md

License

KaTeX is licensed under the MIT License.