shaka-player/lib/util/functional.js

/**
 * @license
 * Copyright 2016 Google Inc.
 *
 * 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.
 */

goog.provide('shaka.util.Functional');


/**
 * @summary A set of functional utility functions.
 */
shaka.util.Functional = class {
  /**
   * Creates a promise chain that calls the given callback for each element in
   * the array in a catch of a promise.
   *
   * e.g.:
   * Promise.reject().catch(callback(array[0])).catch(callback(array[1]));
   *
   * @param {!Array.<ELEM>} array
   * @param {function(ELEM):!Promise.<RESULT>} callback
   * @return {!Promise.<RESULT>}
   * @template ELEM,RESULT
   */
  static createFallbackPromiseChain(array, callback) {
    return array.reduce((promise, elem) => {
      return promise.catch(() => callback(elem));
    }, Promise.reject());
  }


  /**
   * Returns the first array concatenated to the second; used to collapse an
   * array of arrays into a single array.
   *
   * @param {!Array.<T>} all
   * @param {!Array.<T>} part
   * @return {!Array.<T>}
   * @template T
   */
  static collapseArrays(all, part) {
    return all.concat(part);
  }

  /**
   * A no-op function that ignores its arguments.  This is used to suppress
   * unused variable errors.
   * @param {...*} args
   */
  static ignored(...args) {}


  /**
   * A no-op function.  Useful in promise chains.
   */
  static noop() {}


  /**
   * Returns if the given value is not null; useful for filtering out null
   * values.
   *
   * @param {T} value
   * @return {boolean}
   * @template T
   */
  static isNotNull(value) {
    return value != null;
  }
};