inmap.js (2661B)
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 // MODULES // 22 23 var isCollection = require( '@stdlib/assert/is-collection' ); 24 var isFunction = require( '@stdlib/assert/is-function' ); 25 26 27 // MAIN // 28 29 /** 30 * Invokes a function once for each element in a collection and updates the collection in-place. 31 * 32 * ## Notes 33 * 34 * - The invoked function's return value is cached prior to updating a collection. Before updating the collection, a collection must be inspected to ensure that a collection has not been resized during invocation such that an index no longer has a corresponding element in the collection. Were a return value automatically used to update a collection, an input collection could be converted into a sparse data structure. While some might consider this a feature, here, we take stance that a user should be less clever. 35 * 36 * 37 * @param {Collection} collection - input collection 38 * @param {Function} fcn - function to invoke 39 * @param {*} [thisArg] - execution context 40 * @throws {TypeError} first argument must be a collection 41 * @throws {TypeError} second argument must be a function 42 * @returns {Collection} input collection 43 * 44 * @example 45 * function scale( value, index, collection ) { 46 * return value * index; 47 * } 48 * 49 * var arr = [ 1, 2, 3, 4 ]; 50 * 51 * var out = inmap( arr, scale ); 52 * // returns [ 0, 2, 6, 12 ] 53 * 54 * var bool = ( out === arr ); 55 * // returns true 56 */ 57 function inmap( collection, fcn, thisArg ) { 58 var len; 59 var v; 60 var i; 61 if ( !isCollection( collection ) ) { 62 throw new TypeError( 'invalid argument. First argument must be a collection. Value: `'+collection+'`.' ); 63 } 64 if ( !isFunction( fcn ) ) { 65 throw new TypeError( 'invalid argument. Second argument must be a function. Value: `'+fcn+'`.' ); 66 } 67 len = collection.length; 68 for ( i = 0; i < len; i++ ) { 69 v = fcn.call( thisArg, collection[ i ], i, collection ); 70 71 // Account for dynamically resizing a collection... 72 if ( len !== collection.length ) { 73 len = collection.length; 74 } 75 if ( i < len ) { 76 collection[ i ] = v; 77 } 78 } 79 return collection; 80 } 81 82 83 // EXPORTS // 84 85 module.exports = inmap;