Merge pull request #12 from adwaithks/javascript-qna

Adding polyfills for Higher Order Functions in javascript - map(), filter() and reduce()

Author: Jayanti2919

Javascript Polyfills/customFilter.js

@@ -0,0 +1,18 @@
+// polyfill for filter() method
+
+Array.prototype.customFilter = function(callback) {
+    let arr = this;
+    let result = [];
+    for (let i = 0; i < arr.length; i ++) {
+        if(callback(arr[i])) result.push(arr[i]);
+    }
+    return result;
+}
+
+// usage
+
+let array = [1,2,3,4,5];
+let evenNumbers = array.customFilter((num) => {
+    return num % 2 == 0;
+});
+console.log(evenNumbers); // [2, 4]

Javascript Polyfills/customMap.js

@@ -0,0 +1,18 @@
+// polyfill for map() method
+
+Array.prototype.customMap = function(callback) {
+    let arr = this;
+    let result = [];
+    for (let i = 0; i < arr.length; i ++) {
+        result.push(callback(arr[i], i, arr));
+    }
+    return result;
+}
+
+// usage
+
+let array = [1,2,3,4,5];
+let twiceOfEachNumber = array.customMap((num) => {
+    return num * 2;
+});
+console.log(twiceOfEachNumber); // [2, 4, 6, 8, 10]

Javascript Polyfills/customReduce.js

@@ -0,0 +1,19 @@
+// polyfill for reduce() method
+
+Array.prototype.customReduce = function(fn, initialValue = null) {
+    let array = this;
+    let index = initialValue ? 0 : 1;
+    let accumulator = initialValue ? initialValue : array[0];
+    for (let i = index; i < array.length; i ++) {
+        accumulator = fn(accumulator, array[i]);
+    }
+    return accumulator;
+}
+
+// usage
+
+let array = [1,2,3,4,5];
+let sum = array.customReduce((acc, num) => {
+    return acc + num;
+});
+console.log(sum); // 15