August 23, 2021

How to get the index from for-of loop with JavaScript

How to get the index from for-of loop with JavaScript

In this tutorial I will show you two ways that you can get the index when using a for-of loop.

Let's start with the data that I will be using:

const shoppingList = [
  'bread',
  'milk',
  'pie',
  'juice'
]

Option 1: .keys()

The first and easiest way to get the index with a for-of loop is to use the Array's built in keys function, like this:

for (const index of shoppingList.keys()) {
  console.log(`${shoppingList[index]} at ${index}`)
}

If you run the above code, you should have the following output:

bread at 0
milk at 1
pie at 2
juice at 3

Option 2: .entries()

This is my preferred way to get the index in a for-of loop. The main reason why I prefer this way is because it provides additional data, rather than changing the way that I use for-of normally.

In the below code you can see what I mean:

for (const [index, shoppingItem] of shoppingList.entries()) {
  console.log(`${shoppingItem} at ${index}`)
}

Normally with a for-of loop you get the element value and not the element index. But using entries you can get both.

If you run the above code, you should have the following output:

bread at 0
milk at 1
pie at 2
juice at 3

Conclusion

I found getting the index in a for-of loop a bit unintuitive, but, after playing around with it a bit, it is quite straight forward.

If you found this article helpful, please consider sharing it with others that could also find it helpful.

You can find my full code here.