Source: lib/util/functional.js

  1. /**
  2.  * @license
  3.  * Copyright 2016 Google Inc.
  4.  *
  5.  * Licensed under the Apache License, Version 2.0 (the "License");
  6.  * you may not use this file except in compliance with the License.
  7.  * You may obtain a copy of the License at
  8.  *
  9.  *     http://www.apache.org/licenses/LICENSE-2.0
  10.  *
  11.  * Unless required by applicable law or agreed to in writing, software
  12.  * distributed under the License is distributed on an "AS IS" BASIS,
  13.  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  14.  * See the License for the specific language governing permissions and
  15.  * limitations under the License.
  16.  */
  18. goog.provide('shaka.util.Functional');
  21. /**
  22.  * @namespace shaka.util.Functional
  23.  * @summary A set of functional utility functions.
  24.  */
  27. /**
  28.  * Creates a promise chain that calls the given callback for each element in
  29.  * the array in a catch of a promise.
  30.  *
  31.  * e.g.:
  32.  * Promise.reject().catch(callback(array[0])).catch(callback(array[1]));
  33.  *
  34.  * @param {!Array.<ELEM>} array
  35.  * @param {function(ELEM):!Promise.<RESULT>} callback
  36.  * @return {!Promise.<RESULT>}
  37.  * @template ELEM,RESULT
  38.  */
  39. shaka.util.Functional.createFallbackPromiseChain = function(array, callback) {
  40.   return array.reduce(function(callback, promise, elem) {
  41.     return promise.catch(callback.bind(null, elem));
  42.   }.bind(null, callback), Promise.reject());
  43. };
  46. /**
  47.  * Returns the first array concatenated to the second; used to collapse an
  48.  * array of arrays into a single array.
  49.  *
  50.  * @param {!Array.<T>} all
  51.  * @param {!Array.<T>} part
  52.  * @return {!Array.<T>}
  53.  * @template T
  54.  */
  55. shaka.util.Functional.collapseArrays = function(all, part) {
  56.   return all.concat(part);
  57. };
  60. /**
  61.  * A no-op function.  Useful in promise chains.
  62.  */
  63. shaka.util.Functional.noop = function() {};
  66. /**
  67.  * Returns if the given value is not null; useful for filtering out null values.
  68.  *
  69.  * @param {T} value
  70.  * @return {boolean}
  71.  * @template T
  72.  */
  73. shaka.util.Functional.isNotNull = function(value) {
  74.   return value != null;
  75. };
  78. /**
  79.  * Creates a function that returns whether the given value is equal to the given
  80.  * value.
  81.  *
  82.  * @param {T} compare
  83.  * @return {function(T):boolean}
  84.  * @template T
  85.  */
  86. shaka.util.Functional.isEqualFunc = function(compare) {
  87.   return function(a) { return a == compare; };
  88. };
  91. /**
  92.  * Creates a function that returns whether the given value is not equal to the
  93.  * given value.
  94.  *
  95.  * @param {T} compare
  96.  * @return {function(T):boolean}
  97.  * @template T
  98.  */
  99. shaka.util.Functional.isNotEqualFunc = function(compare) {
  100.   return function(a) { return a != compare; };
  101. };