Index inside map function

Question

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   gt    a  mapper a  b  mapper index       toList      Documentation shows that map   returns Iterable lt number  M gt   Is there any elegant way to what I need

User · Accepted Answer

You will be able to get the current iteration's index for the map method through its 2nd parameter.

Example:

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

Output:

The current iteration is: 0 <br>The current element is: h

The current iteration is: 1 <br>The current element is: e

The current iteration is: 2 <br>The current element is: l

The current iteration is: 3 <br>The current element is: l 

The current iteration is: 4 <br>The current element is: o

See also: https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Array/map

Parameters

callback - Function that produces an element of the new Array, taking three arguments:

1) currentValue
The current element being processed in the array.

2) index
The index of the current element being processed in the array.

3) array
The array map was called upon.

User · Answer

Using Ramda   import  addIndex  map  from  ramda    const list      h    e    l    l    o    const mapIndexed   addIndex map   mapIndexed  currElement  index    gt      console log  The current iteration is      index     console log  The current element is      currElement     console log   n      return  X      list

User · Answer

Array prototype map   index   One can access the index Array prototype map   via the second argument of the callback function  Here is an example    x000D   x000D  const array    1  2  3  4   x000D   x000D   x000D  const map   array map  x  index    gt    x000D    console log index   x000D    return x   index  x000D      x000D   x000D  console log map   x000D   x000D   x000D    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    x000D   x000D  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   x000D   x000D   x000D

User · Answer

suppose you have an array like   x000D   x000D     const arr    1  2  3  4  5  6  7  8  9                arr map  myArr  index    gt          console log  your index is - gt    index  AND value is   myArr            x000D   x000D   x000D    gt  output will be  index is - gt  0 AND value is 1  index is - gt  1 AND value is 2  index is - gt  2 AND value is 3  index is - gt  3 AND value is 4  index is - gt  4 AND value is 5  index is - gt  5 AND value is 6  index is - gt  6 AND value is 7  index is - gt  7 AND value is 8  index is - gt  8 AND value is 9

[javascript] Index inside map() function

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