Array polyfills: map, filter, reduce, every

EasyJavaScript

Was this asked in an interview?

Very frequently asked. Write custom polyfills for map, filter, reduce, and every. reduce is the most important.

Problem

Implement polyfills for the core array methods as Array.prototype.myMap, myFilter, myReduce, and myEvery. Match the native callback signature (element, index, array) and, for reduce, the optional initialValue.

Array.prototype.myMap = function (callback, thisArg) {
  // your code
};

Array.prototype.myFilter = function (callback, thisArg) {
  // your code
};

Array.prototype.myReduce = function (callback, initialValue) {
  // your code
};

Array.prototype.myEvery = function (callback, thisArg) {
  // your code
};