com.google.javascript.jscomp.js.es6.util.iteratorfromarray.js Maven / Gradle / Ivy

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/*
 * Copyright 2016 The Closure Compiler Authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

/**
 * @fileoverview Utilities for iterator-returning methods.
 */
'require es6/symbol';


/**
 * Creates an iterator from an array-like, with a transformation function.
 * @param {!IArrayLike} array
 * @param {function(number, INPUT): OUTPUT} transform
 * @return {!IteratorIterable}
 * @template INPUT, OUTPUT
 * @suppress {checkTypes|reportUnknownTypes}
 */
$jscomp.iteratorFromArray = function(array, transform) {
  // NOTE: IE8 doesn't support indexing from boxed Strings.
  if (array instanceof String) array = array + '';
  var i = 0;
  var done = false;
  var iter = {
    next: function() {
      // Once we return done, we must always return done, even if the array
      // grows later.
      if (!done && i < array.length) {
        var index = i++;
        return {value: transform(index, array[index]), done: false};
      }
      done = true;
      return {done: true, value: void 0};
    }
  };
  iter[Symbol.iterator] = function() { return iter; };
  return iter;
};