Write a polyfill for Array.map in javascript

What is Aray.map?

Array.map accepts a callback function, executes the same over the original array and returns a new array.

//Example: const arr = ar1.map(x => x*2)

What do we need a polyfill?

We need polyfills to support the old browsers for the new methods like Array.map etc. introduced in the latest ecmascript.

Polyfill for Array.map

Lets write a polyfill named myMap.

Note: "this" will contain the original array passed through the polyfill function.

function myMap(fun) {

if (this === null || this === undefined) {

console.log('myMap is iterating over an empty list.');

}

// validating function

if (typeof fun !== 'function') {

console.log('myMap is missing the callback function as a parameter.');

}

// get the original array

var oArray = this;

let output = [];

console.log('original array: ', this, arguments);

oArray.forEach((item) => {

output.push(fun(item));

});

return output;

}

Array.prototype.myMap = myMap;

let arr = [1, 2, 3];

console.log('New array: ', arr.myMap(x => x*2)); // [2,4,6];

Read other such interview questions with solutions in my blog.

Abhijit Padhy