indexesOf: collect all indexes of pattern found in string.

indexesof.js

// Returns an array of all indexes at which `pattern` can be found in `string`.
function indexesOf(string, pattern) {
  var i = -1;
  var indexes = [];
  // We mutate `i` in place with the result of `indexOf`. We also use the last
  // value of `i + 1` to continue seeking from. Any index found is pushed into
  // the `indexes` array. If we ever get `-1` as the result of `indexOf`, we
  // stop looping.
  while((i = string.indexOf(pattern, i + 1)) !== -1) indexes.push(i);
  return indexes;
}