src/common/fast-path.js/FastPath/map
class FastPath:  map(callback, ...names) {
    const { stack } = this;
    const { length } = stack;
    let value = getLast(stack);

    for (const name of names) {
      value = value[name];
      stack.push(name, value);
    }

    const result = new Array(value.length);

    for (let i = 0; i < value.length; ++i) {
      if (i in value) {
        stack.push(i, value[i]);
        result[i] = callback(this, i);
        stack.length -= 2;
      }
    }

    stack.length = length;

    return result;
  }