How to find the index of an element in an array in JavaScript

Finding the index position of elements in arrays is essential for data manipulation, conditional logic, and implementing features like highlighting, sorting, or removing specific items in JavaScript applications. With over 25 years of experience in software development and as the creator of CoreUI, I’ve implemented index searching extensively in components like sortable lists, selection systems, and data tables where precise element positioning is crucial. From my extensive expertise, the most straightforward and efficient solution is using the indexOf() method for primitive values, which returns the first occurrence’s index. This approach is fast, widely supported, and specifically designed for finding element positions.

Use the indexOf() method to find the index position of an element in an array.

const fruits = ['apple', 'banana', 'orange', 'banana']
const index = fruits.indexOf('banana')
// Result: 1

The indexOf() method searches the array from the beginning and returns the index of the first occurrence of the specified element, or -1 if the element is not found. In this example, fruits.indexOf('banana') returns 1 because ‘banana’ first appears at index 1. The method uses strict equality (===) for comparison, so it works reliably with strings, numbers, and booleans. If you need to find the last occurrence, use lastIndexOf() instead, or for complex objects, use findIndex() with a custom comparison function.

Best Practice Note:

This is the same approach we use in CoreUI components for managing active states and element positioning in navigation systems. For finding indices based on complex conditions, use findIndex(): array.findIndex(item => item.id === targetId). Always check if the returned index is not -1 before using it to avoid errors when the element doesn’t exist.