How to Get Index Inside map() in JavaScript


How can we get the index of the current iteration inside a map() function?

Example scenario#

Suppose we have an array we want to iterate over using the map() function.

const lst = [1, 2, 3];
lst.map((elem) => {
  console.log(`Element: ${elem}`);
  return elem;
});

How can we access the index of the current iteration inside the map() callback function? Without a for loop, this process isn’t as intuitive without reading the docs.

Getting the index in map()#

We can get the index of the current iteration using the 2nd parameter of the map() function.

const lst = [1, 2, 3];
lst.map((elem, index) => {
  console.log(`Element: ${elem}`);
  console.log(`Index: ${index}`);
  return elem;
});

From the MDN Web Docs, the following are the parameters for the map() function.

  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.