Lesson 68 - Replacing & Modifying Strings with Regex

Regular expressions (regex) are useful not only for searching and matching patterns in strings but also for replacing and modifying text dynamically. In JavaScript, the replace() method is commonly used with regex to replace parts of a string.

The replace() Method

The replace() method allows us to replace occurrences of a substring or pattern within a string. When combined with regex, it becomes a powerful tool for text manipulation.

Syntax:

string.replace(pattern, replacement)

• pattern: A string or a regular expression to match.
• replacement: The new string that replaces the matched value.

Basic Example: Replacing a Word

let text = "JavaScript is awesome!";
let newText = text.replace("awesome", "powerful");

console.log(newText); // Output: JavaScript is powerful!

Using Regex for Case-Insensitive Replacement

The i flag makes the search case-insensitive.

let text = "JavaScript is Awesome!";
let newText = text.replace(/awesome/i, "powerful");

console.log(newText); // Output: JavaScript is powerful!

Replacing Multiple Occurrences

The g flag (global flag) ensures all matches are replaced, not just the first one.

let text = "I love JavaScript. JavaScript is fun!";
let newText = text.replace(/JavaScript/g, "JS");

console.log(newText); // Output: I love JS. JS is fun!

Using Capture Groups in Replacement

You can use parentheses () to capture parts of the matched string and reference them in the replacement using $1, $2, etc.

let text = "Hello, Mr. John Doe";
let newText = text.replace(/Mr\. (\w+) (\w+)/, "Mr. $2, $1");

console.log(newText); // Output: Hello, Mr. Doe, John

Removing Unwanted Characters

Regex can be used to remove unwanted characters, such as special symbols:

let text = "Hello! How are you? #greetings";
let newText = text.replace(/[^a-zA-Z0-9 ]/g, "");

console.log(newText); // Output: Hello How are you greetings

Try Your Hand

1. Write a JavaScript function that replaces all numbers in a string with X.
2. Modify a string to swap the first and last words using regex.