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, and IE 8 - IE 11. A list of supported commands can be on the wiki.