The RegExp object in JavaScript is a powerful tool for pattern matching, searching, and manipulating strings. It allows you to define patterns for matching text and helps in validation, extraction, and replacement.

1. String Searching

Check if a String Contains a Word

let s = "Welcome to JavaScript!";
let regex = /JavaScript/;
console.log(regex.test(s));

let s = "Welcome to JavaScript!";

let regex = /JavaScript/;

console.log(regex.test(s));

true

Case-Insensitive Search

let s = "Learning javascript is fun!";
let regex = /JavaScript/i;
console.log(regex.test(s));

let s = "Learning javascript is fun!";

let regex = /JavaScript/i;

console.log(regex.test(s));

true

2. String Validation

Validate an Email Address

let mail = "user@example.com";
let regex = /^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$/;
console.log(regex.test(mail));

let mail = "user@example.com";

let regex = /^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$/;

console.log(regex.test(mail));

true

Validate a Password

let pass = "P@ssw0rd";
let regex = /^(?=.*[A-Za-z])(?=.*\d)(?=.*[@$!%*?&])[A-Za-z\d@$!%*?&]{8,}$/;
console.log(regex.test(pass));

let pass = "P@ssw0rd";

let regex = /^(?=.*[A-Za-z])(?=.*\d)(?=.*[@$!%*?&])[A-Za-z\d@$!%*?&]{8,}$/;

console.log(regex.test(pass));

true

3. Pattern Matching and Extraction

Extract Phone Numbers

let s = "Call me at 123-456-7890 or 987-654-3210.";
let regex = /\d{3}-\d{3}-\d{4}/g;
console.log(s.match(regex));

let s = "Call me at 123-456-7890 or 987-654-3210.";

let regex = /\d{3}-\d{3}-\d{4}/g;

console.log(s.match(regex));

[ '123-456-7890', '987-654-3210' ]

Extract Domain Names from Emails

let mails = "user1@example.com, user2@test.org";
let regex = /@(\w+\.\w+)/g;
let a = [];
let match;
while ((match = regex.exec(mails)) !== null) {
    a.push(match[1]);
}
console.log(a);

let mails = "user1@example.com, user2@test.org";

let regex = /@(\w+\.\w+)/g;

let a = [];

let match;

while ((match = regex.exec(mails)) !== null) {

    a.push(match[1]);

}

console.log(a);

[ 'example.com', 'test.org' ]

4. Search and Replace

Replace All Occurrences of a Word

let s1 = "JavaScript is fun. JavaScript is powerful.";
let s2 = s1.replace(/JavaScript/g, "JS");
console.log(s2);

let s1 = "JavaScript is fun. JavaScript is powerful.";

let s2 = s1.replace(/JavaScript/g, "JS");

console.log(s2);

JS is fun. JS is powerful.

Sanitize Input by Removing Special Characters

let s1 = "Hello@World#2024!";
let s2 = s1.replace(/[!@#]/g, "");
console.log(s2);

let s1 = "Hello@World#2024!";

let s2 = s1.replace(/[!@#]/g, "");

console.log(s2);

HelloWorld2024

5. Dynamic Pattern Matching

Highlight User Input in Text

let s1 = "JavaScript is awesome!";
let s2 = "javascript";
let regex = new RegExp(s2, "i");
console.log(s1.replace(regex, "**JavaScript**"));

let s1 = "JavaScript is awesome!";

let s2 = "javascript";

let regex = new RegExp(s2, "i");

console.log(s1.replace(regex, "**JavaScript**"));

**JavaScript** is awesome!

Built-In Methods of RegExp

• test(): Checks if a pattern exists in a string.
• exec(): Executes a search for a match and returns details about the match.
• match(): Used with strings to find matches.
• replace(): Replaces matched text with new content.

Real-World Use Cases

• Form Validation: Ensure user inputs match required formats, like emails, phone numbers, or passwords.
• Log Parsing: Extract data like IP addresses, error messages, or timestamps from server logs.
• Dynamic Search and Highlighting: Enable search functionality with user-defined patterns, like search filters in applications.
• Data Cleaning: Remove unwanted characters or transform text into standardized formats.
• Web Scraping: Extract meaningful data from raw HTML or web content for analysis.