indexOf

The indexOf() method returns the index of the first occurrence of a substring in a string, or undefined if the substring is not found.

Interactive example

Syntax

Classic signature

function indexOf(
	input: string, 
	searchString: string, 
	position?: number
): number | undefined;

Curried signature

function indexOf<
	GenericInput extends string
>(
	searchString: string
): (input: GenericInput) => number | undefined;

Parameters

• input: The string in which to search.
• searchString: The substring to search for.
• position (optional): The position in the string from which to start searching. Defaults to 0.

Return value

The index of the first occurrence of the substring, or undefined if the substring is not found.

See also

• includes: Checks whether a string contains a substring.
• search: Searches for a match with a regular expression.
• match: Retrieves matches of a string with a regular expression.

Sources

• MDN Web Docs: String.prototype.indexOf()