Getting the last matching item in an array with vanilla JS

The Array.indexOf() method returns the index of the first item in an array that matches the value you’ve provided (or -1 if it’s not found).

var wizards = ['Harry', 'Hermione', 'Neville', 'Ron', 'Hermione', 'Gandalf', 'Neville'];

// Find "Neville"
// returns 2
wizards.indexOf('Neville');

// Find "Radagast"
// returns -1
wizards.indexOf('Radagast');

But what if you want to find the last matching item in an array?

The Array.lastIndexOf() method

As the name implies, the Array.lastIndexOf() method returns the index of the last matching item in an array, or -1 if a match is not found.

// Find "Neville"
// returns 6
wizards.lastIndexOf('Neville');

// Find "Radagast"
// returns -1
wizards.lastIndexOf('Radagast');

Here’s a demo.

Starting at a specific index

The Array.lastIndexOf() method accepts a second argument: fromIndex.

It defaults to the index of last item in the array (array.length - 1). If you pass in a positive integer, it will start that many items from the start of the array. If you pass in a negative integer, it will start that many items from the end.

// This skips the item at index 6 because it starts at index 4
// returns 2
wizards.lastIndexOf('Neville', 4);

// This starts with index 5 (two in from the last item)
// returns 4
wizards.lastIndexOf('Hermione', -2);

Here’s another demo.

Browser compatibility

The Array.lastIndexOf() method works in all modern browsers, and IE9 and above.