JavaScript (ES2026) reference · String Methods

JavaScript String indexOf() Method

Return the index of the first occurrence of some text, or -1 if it isn't found.

JavaScript (ES2026) Since ES1

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Syntax

string.indexOf(searchString, position)

Parameter	Description
`searchString`	Text to look for.
`position` optional	Index to start from. Default: `0`

An index, or -1.

Find positionsTry it yourself

const s = "banana";
console.log(s.indexOf("an"), s.indexOf("an", 2), s.indexOf("x"));

Output

1 3 -1

Split around a characterTry it yourself

const email = "[email protected]";
const at = email.indexOf("@");
console.log(email.slice(0, at), email.slice(at + 1));

Output

ada example.com

Version	Change
JavaScript ES1	Added

string.lastIndexOf() · Return the index of the last occurrence of some text, searching backwards, or -1 if it isn't found.
string.includes() · Return true if the string contains the given text anywhere. Case-sensitive.
string.search() · Return the index of the first regular-expression match, or -1 if there is none.
JavaScript Strings · tutorial
JavaScript String Methods · tutorial