parse-katex

Parses all HTML code and renders all LaTeX code (by default marked by $ ... $ for inline equations, and $$ ... $$ for display mode) to properly formatted expressions using KaTeX.

The benefit to using this package is you can pre-render all math content (when it is called from the database for instance) and serve it to the user as pure HTML, which is faster, doesn't cause the page to flicker/rearrange on load, and doesn't need them to have JavaScript enabled.

There is also an Express.js template engine for serving views in an Express app.

To install, run npm install --save parse-katex.

Then, to use simply include it, and then call the function renderLaTeX(code, [config]) (or render which is an alias) like such:

var katex = require('parse-katex');
var console = require('console');
    
console.log(katex.renderLaTeX("<p>This is a sentence with an equation $a^2 + b^2 = c^2$</p>"));

On the user facing page, you still need to include the KaTeX CSS file (you don't need to include the KaTeX JavaScript file) to cause it to render properly. You can include it like this:

<link rel="stylesheet" href="//cdnjs.cloudflare.com/ajax/libs/KaTeX/0.2.0/katex.min.css">

You can custom the delimiters that are used to render the code by specifying them in the config section as such:

var config = [['~~', '\~\~', true], ['~', '\~', false]]
var parsedHTML = katex.render('<p>This is a test sentence with an equation ~a^2 = 99~.</p>', config)

Note that to use custom delimiters you need to specify an array in order of which they will evaluate (usually you want to evaluate the display mode math first if it is double the symbol of the inline math), and specify the delimiter, the escaped version of the delimiter, and a boolean specifying whether you want to render it as display (true) or inline (false) math.

To use the Express.js template engine, simply use the katex.templateEngine function to declare the engine. The following example shows a minimal setup to render KaTeX in html files (note that the stylesheet is automatically appended to the head when using the template engine so there is no need to include it manually).

var express = require('express');
var katex = require('parse-katex');

var app = express();

app.engine('html', katex.templateEngine);
app.set('view engine', 'html');

app.get('/', function(req, res, next) {
  return res.render('index');
});

app.listen(3000);