Tiny automatic KaTeX rendering.

katex_auto.js

// Automatically render all elements of type pre.math as latex equations.
(function() {
    var math_elements = document.querySelectorAll('pre.math');

    math_elements.forEach(function(e) {
        e.innerHTML = katex.renderToString(e.innerText);
    });
})();

In my opinion, this is significantly better than using the massive auto-render.js that KaTeX provides. You don't get the convenience of automatically rending LaTeX inside of text blocks, but you save over 10KB and an extra HTTP request.