partition() - Partitions a string by using the given delimiter. In other words this splits a string while keeping the substring matches that were used to delimit the string.

partition.js

/**
 * Partitions a string by using the given delimiter.
 * @param {string} string
 * @param {string|RegExp} delimiter 
 * @returns {(string | (string[] & {input: string, index: number, groups?: Record<string,string>}))[]}
 *   All items of an even index in the zero-indexed array will be strings while
 *   all items of an odd index will be `RegExpMatchArray` objects.
 */
function partition(string, delimiter) {
  const parts = [];
  string.replaceAll(
    ('string' !== typeof delimiter && !delimiter.global)
      ? new RegExp(delimiter.source, delimiter.flags + 'g')
      : delimiter,
    function(...array) {
      let last = array.pop(0);
      let isLastInput = 'string' === typeof last;
      array.input = isLastInput ? last : array.pop(0);
      array.groups = isLastInput ? undefined : last;
      array.index = array.pop(0);
      parts.push(array);
    }
  );
  let end = string.length;
  for (let partsIndex = parts.length; -1 < partsIndex--;) {
    let part = parts[partsIndex];
    let nextEnd = part ? part.index : 0;
    let start = part ? nextEnd + part[0].length : 0;
    parts.splice(partsIndex + 1, 0, string.slice(start, end));
    end = nextEnd;
  }
  return parts;
}

~example-run.js

console.log(partition('hello crazy world!', ' '));
console.log(partition('hello \xA0 crazy,\nlazy world!', /\s+/));