index.js

/* Process inline math */
/*
Like markdown-it-simplemath, this is a stripped down, simplified version of:
https://github.com/runarberg/markdown-it-math

It differs in that it takes (a subset of) LaTeX as input and relies on KaTeX
for rendering output.
*/

/*jslint node: true */
'use strict';

var katex = require('katex');

// Test if potential opening or closing delimieter
// Assumes that there is a "$" at state.src[pos]
function isValidDelim(state, pos) {
    var prevChar, nextChar,
        max = state.posMax,
        can_open = true,
        can_close = true;

    prevChar = pos > 0 ? state.src.charCodeAt(pos - 1) : -1;
    nextChar = pos + 1 <= max ? state.src.charCodeAt(pos + 1) : -1;

    // Check non-whitespace conditions for opening and closing, and
    // check that closing delimeter isn't followed by a number
    if (prevChar === 0x20/* " " */ || prevChar === 0x09/* \t */ ||
            (nextChar >= 0x30/* "0" */ && nextChar <= 0x39/* "9" */)) {
        can_close = false;
    }
    if (nextChar === 0x20/* " " */ || nextChar === 0x09/* \t */) {
        can_open = false;
    }

    return {
        can_open: can_open,
        can_close: can_close
    };
}

function math_inline(state, silent) {
    var start, match, token, res, pos, esc_count;

    if (state.src[state.pos] !== "$") { return false; }

    res = isValidDelim(state, state.pos);
    if (!res.can_open) {
        if (!silent) { state.pending += "$"; }
        state.pos += 1;
        return true;
    }

    // First check for and bypass all properly escaped delimieters
    // This loop will assume that the first leading backtick can not
    // be the first character in state.src, which is known since
    // we have found an opening delimieter already.
    start = state.pos + 1;
    match = start;
    while ( (match = state.src.indexOf("$", match)) !== -1) {
        // Found potential $, look for escapes, pos will point to
        // first non escape when complete
        pos = match - 1;
        while (state.src[pos] === "\\") { pos -= 1; }

        // Even number of escapes, potential closing delimiter found
        if ( ((match - pos) % 2) == 1 ) { break; }
        match += 1;
    }