@rbxts/jsnatives

indexOf

Returns the index of the first occurrence of a specified value in a string.

Signature

function indexOf(str: string, search: PatternAdmissible, position?: NumericAdmissible): number

Description

The indexOf function returns the position of the first occurrence of a specified value in a string. The search begins at the specified position and is case-sensitive.

If the specified value is not found, it returns -1.

Parameters

str: The string to search within.
search: The value to search for. Can be a string, number, or boolean.
position (optional): The position within the string to start the search. Default is 0. If a string is provided, it will be converted to a number.

Return value

The zero-based index of the first occurrence of the specified value.
If the value is not found, -1 is returned.

Examples

Basic usage

// Find the first occurrence of a substring
const pos = String.indexOf("Hello world", "world");
print(pos); // Outputs: 6

// Searching for a character
const letterPos = String.indexOf("Hello world", "o");
print(letterPos); // Outputs: 4

With starting position

// Start searching from index 5
const str = "Hello world, welcome to the universe";
const pos = String.indexOf(str, "world", 5);
print(pos); // Outputs: 6

// Start searching after the first occurrence
const firstPos = String.indexOf(str, "e");
print(firstPos); // Outputs: 1

const secondPos = String.indexOf(str, "e", firstPos + 1);
print(secondPos); // Outputs: 8

Using non-string search values

// Searching for a number (converted to string)
const numPos = String.indexOf("Value: 42 is the answer", 42);
print(numPos); // Outputs: 7

// Searching for a boolean (converted to string)
const boolPos = String.indexOf("Is it true or false?", true);
print(boolPos); // Outputs: 6

Not found cases

// Searching for a value that doesn't exist
const notFound = String.indexOf("Hello world", "xyz");
print(notFound); // Outputs: -1

// Starting search beyond where the value exists
const tooFar = String.indexOf("Hello world", "Hello", 2);
print(tooFar); // Outputs: -1

Case-sensitive search

// Searches are case-sensitive
const lowerCase = String.indexOf("Hello World", "world");
print(lowerCase); // Outputs: -1 (not found because of case difference)

const exactCase = String.indexOf("Hello World", "World");
print(exactCase); // Outputs: 6