String.prototype.startsWith()

Summary: in this tutorial, you will learn how to use the JavaScript String startsWith() method to perform a case-sensitive search and determine if a string starts with a substring.

Introduction to the JavaScript String startsWith() method

The startsWith() returns true if a string starts with a substring or false otherwise.

Here’s the syntax of the startsWith() method:

String.startsWith(searchString [,position])Code language: JavaScript (javascript)

In this syntax:

• searchString is a substring to search for within the string.
• position is an optional parameter that determines the starting position to search for the searchString.

The position defaults to 0. This means that the method starts searching for the searchString from the beginning of the string.

Like other string methods, the startsWith() method always performs a case-sensitive search.

The startsWith() method throws a TypeError if the searchString is a regular expression.

JavaScript String startsWith() method examples

Let’s take some examples of using the startsWith() method.

Basic JavaScript String startsWith() method

The following example uses the startsWith() method to check if the string "Jack and Jill Went Up the Hill" starts with the substring 'Jack':

const title = "Jack and Jill Went Up the Hill";
const result = title.startsWith("Jack");

console.log({ result });Code language: JavaScript (javascript)

Output:

{ result: true }Code language: CSS (css)

Case-sensitive search example

The startsWith() method always performs a case-sensitive search, so the following statement returns false:

const title = "Jack and Jill Went Up the Hill";
const result = title.startsWith("jack");

console.log({ result });Code language: JavaScript (javascript)

Output:

{ result: false }Code language: CSS (css)

Using the position parameter

This example uses the startsWith() method with the second parameter that specifies the beginning position to start searching:

const title = "Jack and Jill Went Up the Hill";
const result = title.startsWith("Jill", 9);

console.log({ result });Code language: JavaScript (javascript)

Output:

{ result: true }Code language: CSS (css)

Throwing a TypeError

The following example throws a TypeError because the searchString is a regular expression:

const str = "JavaScript";
const result = str.startsWith(/J/);

console.log({ result });Code language: JavaScript (javascript)

Output:

TypeError: First argument to String.prototype.startsWith must not be a regular expressionCode language: JavaScript (javascript)

Summary

• Use JavaScript String startsWith() method to perform a case-sensitive search and check if a string starts with a substring.