code: function forEach(f, arr) {
    if (NATIVE_ARRAY_FOREACH) {
      if (arr) {
        NATIVE_ARRAY_FOREACH.call(arr, f);
      }
  
      return;
    }
  
    for (var i = 0; i < arr.length; i++) {
      f(arr[i], i, arr);
    }
  }
docs: Loop a function over an object, for side-effects.
  @param {object} obj The object.
  @param {function} f The function.