Regular Expressions in TypeScript with Examples

Regular Expressions in TypeScript: Syntax, Methods, and Examples

Regular expressions (regex) are a powerful tool for working with strings. In TypeScript, they allow you not only to search, replace, and validate text but also to get strict typing of results. In this article, we will cover all aspects of working with RegExp in TypeScript: from basic syntax to advanced techniques with code examples.

1. Creating Regular Expressions in TypeScript

In TypeScript, as in JavaScript, there are two ways to create a regular expression:

Literal Syntax

The most common and convenient way is to use slashes:

const pattern: RegExp = /hello/gi;

Here g is global search, i is case-insensitivity. The RegExp type is inferred automatically, but it can be specified explicitly for readability.

RegExp Constructor

Used when the pattern is formed dynamically:

const searchTerm: string = "world";const dynamicPattern: RegExp = new RegExp(searchTerm, "gi");

The second argument is a string with flags. The return type is RegExp.

2. Basic RegExp and String Methods

TypeScript inherits all JavaScript methods but adds strict typing to them. Let's look at key methods with examples.

The test() Method

Checks if there is a match in the string. Returns boolean.

const emailRegex: RegExp = /^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\\.[a-zA-Z]{2,}$/;const email: string = "user@example.com";

const isValid: boolean = emailRegex.test(email);console.log(isValid); // true

The exec() Method

Searches for a match and returns detailed information. Returns RegExpExecArray | null.

const text: string = "Price: 1500 rubles, discount: 200 rubles";const pricePattern: RegExp = /(\\d+)\\s*rubles/g;

let match: RegExpExecArray | null;while ((match = pricePattern.exec(text)) !== null) {    console.log(`Found: ${match[0]}, number: ${match[1]}`);}// Output:// Found: 1500 rubles, number: 1500// Found: 200 rubles, number: 200

The String match() Method

Works similarly to exec(), but is called on the string. Returns RegExpMatchArray | null.

const phone: string = "Contacts: +7 (999) 123-45-67";const phoneRegex: RegExp = /\\+7\\s*\\(\\d{3}\\)\\s*\\d{3}-\\d{2}-\\d{2}/;

const result: RegExpMatchArray | null = phone.match(phoneRegex);if (result) {    console.log(`Phone found: ${result[0]}`);    // Phone found: +7 (999) 123-45-67}

The replace() Method

Replaces matches with a new string. Returns string. Supports a callback for complex replacements.

function formatDate(input: string): string {    const datePattern: RegExp = /(\\d{4})-(\\d{2})-(\\d{2})/;    return input.replace(datePattern, "$3.$2.$1");}

const isoDate: string = "2025-03-10";const formatted: string = formatDate(isoDate);console.log(formatted); // "10.03.2025"

The split() Method

Splits a string by a regular expression. Returns string[].

const data: string = "apple;pear;orange;banana";const items: string[] = data.split(/;\\s*/);console.log(items); // ["apple", "pear", "orange", "banana"]

3. Flags and Their Combinations

Flags control the behavior of the regular expression. In TypeScript, they are set either in the literal or as the second argument of the constructor.