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ForEach, Map, Filter and Reduce in Javascript
ForEach, Map, reduce, and filter are all array methods in JavaScript. Map, reduce, and filter will iterate over an array and perform a transformation or computation and return some value while ForEach is used to just iterate over an array.
ForEach: ForEach method executes a provided function once for each array element.
ex: let arrA = [1,2,3,4]arrA.forEach(element => console.log(element));// [1,2,3,4]Map: Execute on each element of array and return new array with same length.
let arrA = [1,2,3,4]let arrB = arrA.map(_i => i*2)console.log(arrB)// [1,4,6,8]Filter: Filter basically return new array with elements which satisfy condition or filter out the elements which not satisfy the condition.
let arrA = [1,2,3,4]let arrB = arrA.filter(_i => i%2)console.log(arrB)// [2,4]Reduce: Reduce basically return a single value. While using it we have do define a initial value of accumulator and in each iteration we have to perform some operation and that will be added to accumulator.
let arrA = [1,2,3,4]let initialVal=0let result = arrA.reduce((accu, val) => val + accu , initialVal);console.log(result)// 10Polyfill for ForEach, Map, Filter and Reduce
A polyfill is a piece of code (usually JavaScript on the Web) used to provide modern functionality on older browsers that do not natively support it.
Array.prototype.customForEach = function(callback) { for (var i = 0; i < this.length; i++) callback(this[i], i, this);};Array.prototype.customMap = function(callback) { arr = []; for (var i = 0; i < this.length; i++) arr.push(callback(this[i], i, this)); return arr;};Array.prototype.customFilter = function(callback, context) { arr = []; for (var i = 0; i < this.length; i++) { if (callback.call(context, this[i], i, this)) arr.push(this[i]); } return arr;};Array.prototype.customReduce = function(callback, initialVal) { var accum = (initialVal === undefined) ? undefined : initialVal; for (var i = 0; i < this.length; i++) { if (accum !== undefined){ accum = callback.call(undefined, accum, this[i], i, this); } else{ accum = this[i]; } } return accum;};Original Link: https://dev.to/unalo_baayriyo/foreach-map-filter-and-reduce-in-javascript-gi9
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