reduce.js (2108B)
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 * Applies a function against an accumulator and each element in a collection and returns the accumulated result. 31 * 32 * @param {Collection} collection - input collection 33 * @param {*} initial - initial value 34 * @param {Function} reducer - reduction function 35 * @param {*} [thisArg] - reduction function execution context 36 * @throws {TypeError} first argument must be a collection 37 * @throws {TypeError} third argument must be a function 38 * @returns {*} accumulated result 39 * 40 * @example 41 * function sum( acc, value ) { 42 * return acc + value; 43 * } 44 * 45 * var arr = [ 1, 2, 3, 4 ]; 46 * 47 * var s = reduce( arr, 0, sum ); 48 * // returns 10 49 */ 50 function reduce( collection, initial, reducer, thisArg ) { 51 var len; 52 var acc; 53 var i; 54 if ( !isCollection( collection ) ) { 55 throw new TypeError( 'invalid argument. First argument must be a collection. Value: `'+collection+'`.' ); 56 } 57 if ( !isFunction( reducer ) ) { 58 throw new TypeError( 'invalid argument. Third argument must be a function. Value:`'+reducer+'`.' ); 59 } 60 len = collection.length; 61 acc = initial; 62 for ( i = 0; i < len; i++ ) { 63 acc = reducer.call( thisArg, acc, collection[ i ], i, collection ); 64 65 // Account for dynamically resizing a collection... 66 if ( len !== collection.length ) { 67 len = collection.length; 68 } 69 } 70 return acc; 71 } 72 73 74 // EXPORTS // 75 76 module.exports = reduce;