A simple javascript, css, html tokenizer/lexer. Taken from @lrsjng/lolight - Lightweight tokenizer and syntax highlighter. https://larsjung.de/lolight/

simple-javascript-css-html-tokenizer.js

 /**
  *  Code taken from @lrsjng/lolight - Lightweight tokenizer and syntax highlighter. 
  *  https://larsjung.de/lolight/
  */
 var KEYWORD_RE = /^(a(bstract|lias|nd|rguments|rray|s(m|sert)?|uto)|b(ase|egin|ool(ean)?|reak|yte)|c(ase|atch|har|hecked|lass|lone|ompl|onst|ontinue)|de(bugger|cimal|clare|f(ault|er)?|init|l(egate|ete)?)|do|double|e(cho|ls?if|lse(if)?|nd|nsure|num|vent|x(cept|ec|p(licit|ort)|te(nds|nsion|rn)))|f(allthrough|alse|inal(ly)?|ixed|loat|or(each)?|riend|rom|unc(tion)?)|global|goto|guard|i(f|mp(lements|licit|ort)|n(it|clude(_once)?|line|out|stanceof|t(erface|ernal)?)?|s)|l(ambda|et|ock|ong)|m(odule|utable)|NaN|n(amespace|ative|ext|ew|il|ot|ull)|o(bject|perator|r|ut|verride)|p(ackage|arams|rivate|rotected|rotocol|ublic)|r(aise|e(adonly|do|f|gister|peat|quire(_once)?|scue|strict|try|turn))|s(byte|ealed|elf|hort|igned|izeof|tatic|tring|truct|ubscript|uper|ynchronized|witch)|t(emplate|hen|his|hrows?|ransient|rue|ry|ype(alias|def|id|name|of))|u(n(checked|def(ined)?|ion|less|signed|til)|se|sing)|v(ar|irtual|oid|olatile)|w(char_t|hen|here|hile|ith)|xor|yield)$/;

var COM = 'com';
var KEY = 'key';
var NAM = 'nam';
var NUM = 'num';
var PCT = 'pct';
var REX = 'rex';
var SPC = 'spc';
var STR = 'str';
var UNK = 'unk';

var TOKEN_RES = [
    [NUM, /#([0-9a-f]{6}|[0-9a-f]{3})\b/],
    [COM, /(\/\/|#).*?(?=\n|$)/],
    [COM, /\/\*[\s\S]*?\*\//],
    [COM, /<!--[\s\S]*?-->/],
    [REX, /\/(\\\/|[^\n])*?\//],
    [STR, /(['"`])(\\\1|[\s\S])*?\1/],
    [NUM, /[+-]?([0-9]*\.?[0-9]+|[0-9]+\.?[0-9]*)([eE][+-]?[0-9]+)?/],
    [PCT, /[\\.,:;+\-*\/=<>()[\]{}|?!&@~]/],
    [SPC, /\s+/],
    [NAM, /[\w$]+/],
    [UNK, /./]
];

var tokenize = function (text) {
    if (typeof text !== 'string') {
        throw new Error('tok: no string');
    }

    var tokens = [];
    var len = TOKEN_RES.length;
    var prefer_div_over_re = false;

    while (text) {
        for (var i = 0; i < len; i += 1) {
            var m = TOKEN_RES[i][1].exec(text);
            if (!m || m.index !== 0) {
                continue;
            }

            var cls = TOKEN_RES[i][0];
            if (cls === REX) {
                continue;
            }

            var tok = m[0];

            if (cls === NAM && KEYWORD_RE.test(tok)) {
                cls = KEY;
            }

            text = text.slice(tok.length);
            tokens.push([cls, tok]);
            break;
        }
    }

    return tokens;
};