码农教程 - 一技在手,衣食无忧! tools

目录

JavaScript Array indexOf()

❮ Previous JavaScript Array Reference Next ❯

Examples

Find the first index of "Apple":

const fruits = ["Banana", "Orange", "Apple", "Mango"];
let index = fruits.indexOf("Apple");
Try it Yourself »

Start at index 3:

const fruits = ["Banana", "Orange", "Apple", "Mango", "Apple"];
let index = fruits.indexOf("Apple", 3);
Try it Yourself »

More examples below.

Description

The indexOf() method returns the first index (position) of a specified value.

The indexOf() method returns -1 if the value is not found.

The indexOf() method starts at a specified index and searches from left to right.

By default the search starts at the first element and ends at the last.

Negative start values counts from the last element (but still searches from left to right).

See Also:

The lastIndexOf() method

Syntax

array.indexOf( item, start)

Parameters

Parameter Description
item Required.
The value to search for.
start Optional.
Where to start the search.
Default value is 0.
Negative values start the search from the end of the array.

Return Value

Type Description
A number The index (position) of the first item found.
-1 if the item is not found.

Note

In an array, the first element has index (position) 0, the second has index 1, ...

More Examples

Find the first index of "Apple", starting from the last element:

const fruits = ["Banana", "Orange", "Apple", "Mango", "Apple"];
let index = fruits.indexOf("Apple", -1);
Try it Yourself »

Related Pages:

Array Tutorial

Array Const

Array Methods

Array Sort

Array Iterations

Browser Support

indexOf() is an ECMAScript5 (ES5) feature.

ES5 (JavaScript 2009) fully supported in all browsers:

Chrome Edge Firefox Safari Opera IE
Yes Yes Yes Yes Yes 9-11


❮ Previous JavaScript Array Reference Next ❯