Implement map on prototype help

Tell us what’s happening:
Doesn’t the map function just make a copy of the original array? If yes, then doesn’t this perform that function appropriately?

Your code so far

// The global variable
var s = [23, 65, 98, 5];

Array.prototype.myMap = function(callback){
var newArray = [];
// Only change code below this line
for (let i = 0; i < s.length; i++){
// Only change code above this line
return newArray;


var new_s = s.myMap(function(item){
return item * 2;

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Challenge: Implement map on a Prototype

Link to the challenge:

no, each element of the new array is changed using the callback function passed as argument of the method

How exactly does the element change? And how do I manage to make that change using a for loop?

you have a function passed as argument of the myMap method: that function is made so that it takes an element from the original array and returns the element to add to the new array

right now you are just pushing the elements to the newArray, you need to change something to instead push the new elements

when you say that I need to push the new elements do you mean the elements that have been multiplied by two?

yes, but you need to make so that it works with any callback function, so you can’t hardcode the multiplication

i couldn’t figure it out on my own. I had to look up the solution. Can you explain to me why they use this.length? Does that just call upon any input that callback happens to be? Why not just use the variable callback and say callback.legnth? and how come you have to use callback(this[i]))?? I’m very confused.

for (let i = 0; i < this.length; i++) {

callback is a function

when you iterate over an array with a for loop you use the iterating variable (in this case i ) that goes from 0 to the length of the array - it is a normal for loop to iterate over an array

you use this to refer to the array on which the method is being used

callback is the function used to change the array elements, so if this[i] is the old array element, callback(this[i]) returns the value you want the new array element to have