slow-json-stringify/src/_makeChunks.mjs

The slowest JSON stringifier in the galaxy (:

/**
 * @param {string} str - prepared string already validated.
 * @param {array} queue - queue containing the property name to match
 * (used for building dynamic regex) needed for the preparation of
 * chunks used in different scenarios.
 */
export default (str, queue) => str
  // Matching prepared properties and replacing with target with or without
  // double quotes.
  // => Avoiding unnecessary concatenation of doublequotes during serialization.
  .replace(/"\w+__sjs"/gm, type => (/string/.test(type) ? '"__par__"' : '__par__'))
  .split('__par__')
  .map((chunk, index, chunks) => {
    // Using dynamic regex to ensure that only the correct property
    // at the end of the string it's actually selected.
    // => e.g. ,"a":{"a": => ,"a":{
    const matchProp = `("${(queue[index] || {}).name}":(\"?))$`;
    const matchWhenLast = `(\,?)${matchProp}`;

    // Check if current chunk is the last one inside a nested property
    const isLast = /^("}|})/.test(chunks[index + 1] || '');

    // If the chunk is the last one the `isUndef` case should match
    // the preceding comma too.
    const matchPropRe = new RegExp(isLast ? matchWhenLast : matchProp);

    // 3 possibilities after arbitrary property:
    // - ", => non-last string property
    // - , => non-last non-string property
    // - " => last string property
    const matchStartRe = /^(\"\,|\,|\")/;

    return {
      // notify that the chunk preceding the current one has not
      // its corresponding property undefined.
      // => This is a V8 optimization as it's way faster writing
      // the value of a property than writing the entire property.
      flag: false,
      pure: chunk,
      // Without initial part
      prevUndef: chunk.replace(matchStartRe, ''),
      // Without property chars
      isUndef: chunk.replace(matchPropRe, ''),
      // Only remaining chars (can be zero chars)
      bothUndef: chunk
        .replace(matchStartRe, '')
        .replace(matchPropRe, ''),
    };
  });