How to Find an Array Index by Value Using JavaScript?

Using indexOf() we can get index of the first matched array element that matches the specified value. If the value does not exist in the array, -1 is returned. For example:

const arr = ['foo', 'bar', 'baz', 'foo', 'qux'];

arr.indexOf('foo'); // 0
arr.indexOf('bar'); // 1
arr.indexOf('baz'); // 2
arr.indexOf('qux'); // 4

arr.indexOf('foobar'); // -1

Similar to indexOf(), we can make use of lastIndexOf() to get index of the last matched array element that matches the specified value. For example:

arr.lastIndexOf('foo'); // 3