Function highlightRegExp

lib/internal/util/inspect.js:535–768

* Colorize a JavaScript RegExp pattern per ECMAScript grammar. * This is a tolerant single-pass highlighter using heuristics in some cases. * It supports: groups (named/unnamed, lookaround), assertions, alternation, * quantifiers, escapes (incl. Unicode properties), character classes and * backr

(regexpString)

 * @returns {string}
 */
function highlightRegExp(regexpString) {
  let out = '';
  let i = 0;
  let depth = 0;
  let inClass = false;

  // TODO(BridgeAR): Add group type tracking. That allows to increase the depth
  // in case the same type is next to each other.
  // let groupType = 0;

  // Verify palette and update cache if user changed colors
  const paletteNames = highlightRegExp.colors?.length > 0 ?
    highlightRegExp.colors :
    highlightRegExpColors;

  const palette = paletteNames.reduce((acc, name) => {
    const color = inspect.colors[name];
    if (color) acc.push([`\u001b[${color[0]}m`, `\u001b[${color[1]}m`]);
    return acc;
  }, []);

  function writeGroup(start, end, decreaseDepth = 1) {
    let seq = '';
    i++;
    // Only checking for the closing delimiter is a fast heuristic for regular
    // expressions without the u or v flag. A safer check would verify that the
    // read characters are all alphanumeric.
    while (i < regexpString.length && regexpString[i] !== end) {
      seq += regexpString[i++];
    }
    if (i < regexpString.length) {
      depth -= decreaseDepth;
      write(start);
      writeDepth(seq, 1, 1);
      write(end);
      depth += decreaseDepth;
    } else {
      // The group is not closed which would lead to mistakes in the output.
      // This is a workaround to prevent output from being corrupted.
      writeDepth(start, 1, -seq.length);
    }
  }

  const write = (str) => {
    const idx = depth % palette.length;
    // Safeguard against bugs in the implementation.
    const color = palette[idx] ?? palette[0];
    out += color[0] + str + color[1];
    return idx;
  };

  function writeDepth(str, incDepth, incI) {
    depth += incDepth;
    write(str);
    depth -= incDepth;
    i += incI;
  }