How to find index in an array of objects in JavaScript

This tutorial is based on using the ES6 Array.findIndex() method to get the first index of an item in an array of objects.

The findIndex() method accepts a callback function as its argument, which iterates through all the elements in the array until the callbackFn does not return a truthy value

Once the callbackFn returns a truthy value, the findIndex() method returns the index of the matched element; otherwise, it returns -1.

The findIndex() method is not supported in IE browsers but you can use a polyfill of Array.findIndex

Find index of an object in an array of objects

In the below example, we will find the index of an object whose one of the keys contains a given value.

const array = [
  { id: 1, city: 'Mumbai'},
  { id: 2, city: 'New York'},
  { id: 3, city: 'Toronto'},
  { id: 4, city: 'London'}
];

const notMatchedIndex = array.findIndex((obj)=>obj.city === 'Berlin');

console.log(notMatchedIndex) // -1

const matchedIndex = array.findIndex((obj)=>obj.city === 'Toronto');

console.log(notMatchedIndex) // 2

Find index of an object using Array.forEach

Array.forEach() method can be used to find the index of an object

const array = [
  { id: 1, city: 'Mumbai'},
  { id: 2, city: 'New York'},
  { id: 3, city: 'Toronto'},
  { id: 4, city: 'London'}
];

function findIndex(array, value) {
  let index = -1;

  array.forEach((obj, i) => {
    if (obj.city === value) {
      index = i;
      return;
    }
  })

  return index;
}

console.log(findIndex(array, 'London'));
 // 3

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