[javascript] Index inside map() function

I am missing a option how to get the index number inside the map function using List from Immutable.js:

var list2 = list1.map(mapper => { a: mapper.a, b: mapper.index??? }).toList();

Documentation shows that map() returns Iterable<number, M>. Is there any elegant way to what I need?

• suppose you have an array like

   const arr = [1, 2, 3, 4, 5, 6, 7, 8, 9]
    
    
    arr.map((myArr, index) => {
      console.log(`your index is -> ${index} AND value is ${myArr}`);
    })

> output will be
 index is -> 0 AND value is 1
 index is -> 1 AND value is 2
 index is -> 2 AND value is 3
 index is -> 3 AND value is 4
 index is -> 4 AND value is 5
 index is -> 5 AND value is 6
 index is -> 6 AND value is 7
 index is -> 7 AND value is 8
 index is -> 8 AND value is 9

Using Ramda:

import {addIndex, map} from 'ramda';

const list = [ 'h', 'e', 'l', 'l', 'o'];
const mapIndexed = addIndex(map);
mapIndexed((currElement, index) => {
  console.log("The current iteration is: " + index);
  console.log("The current element is: " + currElement);
  console.log("\n");
  return 'X';
}, list);

Array.prototype.map() index:

One can access the index Array.prototype.map() via the second argument of the callback function. Here is an example:

const array = [1, 2, 3, 4];_x000D_
_x000D_
_x000D_
const map = array.map((x, index) => {_x000D_
  console.log(index);_x000D_
  return x + index;_x000D_
});_x000D_
_x000D_
console.log(map);

Other arguments of Array.prototype.map():

• The third argument of the callback function exposes the array on which map was called upon
• The second argument of Array.map() is a object which will be the this value for the callback function. Keep in mind that you have to use the regular function keyword in order to declare the callback since an arrow function doesn't have its own binding to the this keyword.

For example:

const array = [1, 2, 3, 4];_x000D_
_x000D_
const thisObj = {prop1: 1}_x000D_
_x000D_
_x000D_
const map = array.map( function (x, index, array) {_x000D_
  console.log(array);_x000D_
  console.log(this)_x000D_
}, thisObj);