@dbl0null/slow-json-stringify/src/_makeChunks.mjs

The slow.. well actually fastest JSON stringifier in the galaxy.

const _replaceString = type => type.indexOf('string') !== -1 ? '"__par__"' : '__par__'

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

const _chunkRegex = /"\w+__sjs"/g

/**
 * @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.
 */
const _makeChunks = (str, queue) => {
  const chunks = str
    // Matching prepared properties and replacing with target with or without
    // double quotes.
    // => Avoiding unnecessary concatenation of doublequotes during serialization.
    .replace(_chunkRegex, _replaceString)
    .split('__par__')
  const result = []

  let _i
  const length = chunks.length
  for (let i = 0; i < length; ++i) {
    const chunk = chunks[i]

    // 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 = `("${queue[i]?.name}":("?))$`

    // Check if current chunk is the last one inside a nested property
    const isLast = (_i = i + 1) === length || (
      (_i = chunks[_i].indexOf('}')) &&
      (_i === 0 || _i === 1)
    )

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

    const withoutInitial = chunk.replace(_matchStartRe, '')

    result.push({
      // 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: withoutInitial,
      // Without property chars
      isUndef: chunk.replace(matchPropRe, ''),
      // Only remaining chars (can be zero chars)
      bothUndef: withoutInitial.replace(matchPropRe, '')
    })
  }

  return result
}

export { _makeChunks }