JavaScript findLastIndex method
last modified April 4, 2025
In this article we show how to find elements in arrays using the
findLastIndex method in JavaScript.
Array element searching
The findLastIndex method searches an array for the last element
that satisfies a provided testing function. It returns the index of the found
element or -1 if no element satisfies the condition.
This method is useful when you need to find the position of the last occurrence
of an element matching specific criteria. Unlike findIndex, which
searches from the start, findLastIndex searches from the end.
The method executes the callback function once for each index of the array in descending order until it finds one where the callback returns a truthy value. If no such element is found, it returns -1.
Basic findLastIndex example
The following example demonstrates the basic usage of the
findLastIndex method.
const numbers = [5, 12, 8, 130, 44, 12]; const isLargeNumber = (element) => element > 10; const lastIndex = numbers.findLastIndex(isLargeNumber); console.log(lastIndex); // Index of last element > 10 console.log(numbers[lastIndex]); // The element itself
We create an array and search for the last element greater than 10. The method returns the index of the last matching element (5 in this case). The original array remains unchanged.
$ node main.js 5 12
Finding last even number
This example shows how to find the index of the last even number in an array.
const nums = [1, 3, 5, 7, 8, 9, 10, 11, 12];
const isEven = (num) => num % 2 === 0;
const lastEvenIndex = nums.findLastIndex(isEven);
console.log(`Last even number at index: ${lastEvenIndex}`);
console.log(`Value: ${nums[lastEvenIndex]}`);
We define an array of numbers and a function to check for even numbers. The
findLastIndex method returns the index of the last even number
(8 in this case). The callback function checks each element from the end.
$ node main.js Last even number at index: 8 Value: 12
Finding last object matching criteria
The findLastIndex method works well with arrays of objects.
const users = [
{ id: 1, name: 'John', active: true },
{ id: 2, name: 'Jane', active: false },
{ id: 3, name: 'Bob', active: true },
{ id: 4, name: 'Alice', active: false }
];
const lastActiveIndex = users.findLastIndex(user => user.active);
console.log(`Last active user at index: ${lastActiveIndex}`);
console.log(users[lastActiveIndex]);
We search an array of user objects for the last active user. The callback checks
the active property of each object. The method returns the index
of the last object where active is true.
$ node main.js
Last active user at index: 2
{ id: 3, name: 'Bob', active: true }
Handling no match found
When no element satisfies the condition, findLastIndex returns -1.
const temperatures = [22, 23, 19, 20, 18];
const isFreezing = (temp) => temp <= 0;
const freezingIndex = temperatures.findLastIndex(isFreezing);
if (freezingIndex === -1) {
console.log('No freezing temperatures found');
} else {
console.log(`Last freezing at index: ${freezingIndex}`);
}
We attempt to find the last freezing temperature in an array. Since none exist, the method returns -1. This example demonstrates proper handling of the no-match case, which is important for robust code.
$ node main.js No freezing temperatures found
Using array element and index in callback
The callback function can access both the element and its index.
const words = ['apple', 'banana', 'cherry', 'date', 'elderberry'];
const isLongWord = (word, index) => {
console.log(`Checking index ${index}: ${word}`);
return word.length > 5;
};
const lastLongWordIndex = words.findLastIndex(isLongWord);
console.log(`Last long word at index: ${lastLongWordIndex}`);
We search for the last long word (length > 5) while logging each check. The callback receives both the element and its index. This demonstrates how the method processes elements from the end of the array.
$ node main.js Checking index 4: elderberry Checking index 3: date Checking index 2: cherry Checking index 1: banana Checking index 0: apple Last long word at index: 4
Source
Array findLastIndex - language reference
In this article we have demonstrated how to use the findLastIndex() method to search arrays in JavaScript from the end.