There are two most important array methods in javascript, Array. Prototype.Map() and Array. Prototype.forEach(), both of these methods are used to iterate over the array but there is a difference between these two methods which creates confusion, let's talk about them.

DEFINITIONS:

The map() method creates a new array populated with the results of calling a provided function on every element in the calling array.

example-

const array = [1,4,9,16]

const map1 = array.map(x => x *2);

console.log(map1);

OUTPUT:- [ 2, 8, 18, 32 ]

This means that the map method will produce a new array. It will always return the same number of items.

Whereas, the forEach() method executes a provided function once for each array element. example-

let friends = ['heena', 'rutkar','sanika'];

friends.forEach(function(e){
    console.log(e);
})

OUTPUT:- 'heena' 'rutkar' 'sanika'

One thing about the map is it returns undefined in the mapped array! let's see an example

let numbers = [1, 2, 3, 4]
let filteredNumbers = numbers.map(function(num, index) {
  if (index < 3) {
     return num
  }
})
// index goes from 0, so the filterNumbers are 1,2,3 and undefined.
// filteredNumbers is [1, 2, 3, undefined]
// numbers is still [1, 2, 3, 4]

##1. Return value: The first difference is the return value of both these methods. The return value of forEach() is undefined, whereas the map() method returns A new array with each element being the result of the callback function. Example:

const numbers = [1,3,5]

const newNumbers = numbers.forEach((e)=>{
    console.log(e);

})
console.log(newNumbers);

return value: undefined

const myArray = [1, 2, 3, 4, 5]
myArray.map(x => x * x)

return value: [1, 4, 9, 16, 25]

2.Chaining other methods:

The second difference is that we can chain different methods like reduce(), sort()...with the map() method, we cannot do the same with forEach() because of its return value undefined. Example:

const arr = [2,4,6,8];

const arr2 = arr.map((e)=> {
    return e*2

}).filter((e)=> {
    return e > 10;
})

console.log(arr2);

OUTPUT:[ 12, 16 ]

3.What to use Map() or forEach()?

If we don't want to use the new generated array further from the map() method, we can prefer to use the forEach() method instead.