TypeScript String indexOf() Method

The indexOf() method in TypeScript is an inbuilt function used to find the index of the first occurrence of a specified value within a calling string. If the value is not found, it returns -1.

Syntax

string.indexOf(searchValue[, fromIndex]) 

Parameter: This method accepts two parameters as mentioned above and described below. 

• searchValue: This parameter is a string representing the value to search for.
• fromIndex: This parameter is a location within the calling string to start the search from.

Return Value: This method returns the index of the found occurrence, otherwise -1 if not found.

The below example illustrates the  String indexOf() method in TypeScriptJS:

Example 1: Finding a Substring

In this example we finds the position of “world” in the string str using indexOf, which returns 21 because world starts at the 21st character (0-based index).

let str: string = "Hello, welcome to the world of TypeScript.";
let index: number = str.indexOf("world");

console.log(index);  // Output: 21

Output: 

21

Example 2: Substring Not Found

In this example we searches for JavaScript in str using indexOf, returning -1 because JavaScript is not found within the string.

let str: string = "Hello, welcome to the world of TypeScript.";
let index: number = str.indexOf("JavaScript");

console.log(index);  // Output: -1

Output: 

-1