main.js (1299B)
1 /** 2 * @license Apache-2.0 3 * 4 * Copyright (c) 2018 The Stdlib Authors. 5 * 6 * Licensed under the Apache License, Version 2.0 (the "License"); 7 * you may not use this file except in compliance with the License. 8 * You may obtain a copy of the License at 9 * 10 * http://www.apache.org/licenses/LICENSE-2.0 11 * 12 * Unless required by applicable law or agreed to in writing, software 13 * distributed under the License is distributed on an "AS IS" BASIS, 14 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 15 * See the License for the specific language governing permissions and 16 * limitations under the License. 17 */ 18 19 'use strict'; 20 21 /** 22 * Tests if a value is `undefined`. 23 * 24 * ## Notes 25 * 26 * - In older browsers, `undefined` is a global which can be overridden. `void`, however, is an operator which **cannot** be overridden. Consequently, better to use `void` to check for `undefined`. See [Stack Overflow][1]. 27 * 28 * [1]: http://stackoverflow.com/a/19369078/2225624 29 * 30 * @param {*} value - value to test 31 * @returns {boolean} boolean indicating whether value is undefined 32 * 33 * @example 34 * var bool = isUndefined( undefined ); 35 * // returns true 36 * 37 * bool = isUndefined( null ); 38 * // returns false 39 */ 40 function isUndefined( value ) { 41 return value === void 0; 42 } 43 44 45 // EXPORTS // 46 47 module.exports = isUndefined;