`Array.prototype.indexOf()`

Returns the first index at which a given element is found, or -1 if absent.

Syntax

arr.indexOf(searchElement, fromIndex)

Name	Type	Required	Description
`searchElement`	`any`	Yes	The value to locate, compared using strict equality (===).
`fromIndex`	`number`	No	Index to start the search from. Negative values count from the end. Defaults to 0.

number — The first matching index, or -1 if not found.

console.log(['a', 'b', 'c', 'b'].indexOf('b'));

Output

console.log([1, 2, 3].indexOf(9));

Output

-1

Uses strict equality, so it cannot find NaN - use `includes` for that. Use `lastIndexOf` to search from the end.