How to Check Whether a String Starts with a Regex in JavaScript

Tutorialsrack 27/02/2022 Jquery Javascript

In this article, you’ll learn how to check whether a string starts with a regex in javascript. We use the test() function to check whether a string starts with a regex or not. 

Make sure your regular expression starts with caret (^), which is a special character that represents the start of the string. 

The test() function will search the string and return true if the string contains a match otherwise, it returns false.

let valid = /^D/.test("Does string start with 'D'.");
//When String Starts with D, it returns true
// Output ==> true

valid = /^D/.test("What a beautiful day.");
//When String Starts Does not with D, it returns false
// Output ==> false

You can also use the new RegExp() constructor to turn a string into a regular expression.

const string = '^Does';
const regex = new RegExp(string);
console.log(regex.test("Does string start with 'Does'."));
// Output ==> true

console.log(regex.test("What a beautiful day."));
// Output ==> false

In your case you're looking for case insensitive, you can add modifiers ‘i’ (case insensitive) as a second parameter with the new regex() constructor. The 'i' flag makes a regular expression case insensitive.

// Output ==> true

// Output ==> true

// Output ==> false

// Or using RegExp constructor
const regexp = new RegExp('^A', 'i');

// Output ==> true

// Output ==> true

// Output ==> false

I hope this article will help you to understand how to check whether a string starts with a regex in javascript.

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