Help me on: Implement map on a Prototype challenge

JavaScript
1

Tell us what’s happening:
Hello everyone, i found the solution on internet, but in fact i can’t understand what is happening with this this.forEach(item => newArray.push(callback(item)));

I can’t understand why using this in this case and how we can access item, if in the parameters we only have callback and not callback(item)

Your code so far


// the global Array
var s = [23, 65, 98, 5];

Array.prototype.myMap = function(callback){
var newArray = [];
// Add your code below this line
this.forEach(item => newArray.push(callback(item)));
// Add your code above this line
return newArray;

};

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

Challenge: Implement map on a Prototype

Link to the challenge:
https://www.freecodecamp.org/learn/javascript-algorithms-and-data-structures/functional-programming/implement-map-on-a-prototype

2

Your code has been blurred out to avoid spoiling a full working solution for other campers who may not yet want to see a complete solution. In the future, if you post a full passing solution to a challenge and have questions about it, please surround it with [spoiler] and [/spoiler] tags on the line above and below your solution code.

Thank you.

3

this is the array on which the myMap method is used

callback is the parameter of myMap, it is a function, and to call it you do it like any function

forEach is an array method, takes a function as parameter (called callback)

item is the parameter of the forEach callback

1 Like
4

Thank you for your advises related to the forum “rules”.

And thank you very very much for your explanation, now i can understand clearly what is happening in the code.