30 Days of JavaScript: Regular Expressions in JavaScript — Day 9

30 Days of Javascript Series by DopeThemes

In the world of coding, you’ll often encounter messy or irregular data. It’s where Regular Expressions, or Regex, step in, a powerful tool that aids in manipulating such data. Regex isn’t a JavaScript-specific concept; in fact, it’s a language in its own right, used across numerous programming languages. Today, we delve into the riveting world of regular expressions in JavaScript.

Before diving into the details, let’s set the stage with an analogy. Think of regular expressions as the “search” function on steroids. They can search for more than just exact matches. They can search for patterns, such as a sequence of numbers or a specific arrangement of characters. Regex is like a detective that uncovers these patterns in your data.

Understanding Regex Patterns

A regular expression pattern consists of simple characters, such as /abc/, or a combination of simple and special characters, like /abc/. In the latter example, the asterisk () is a special character indicating zero or more occurrences of the preceding character. In other words, /ab*c/ matches “ac”, “abc”, “abbc”, and so on.

Let’s explore this concept with some code.

let regexPattern = /ab*c/;
let someString = 'abbbc';
let result = regexPattern.test(someString);
console.log(result); // Outputs: true

In the above code snippet, we’re testing whether someString matches the pattern described by regexPattern. The test() method returns a boolean indicating if the pattern was found.

String Manipulation with Regex

Regex shines in manipulating strings. Imagine you have a lengthy text and you want to replace all occurrences of a word with another one. With regex, it’s a walk in the park!

Let’s see this in action:

let regexPattern = /Javascript/gi;
let text = 'Javascript is the backbone of modern web development. Javascript is powerful.';
let newText = text.replace(regexPattern, 'JavaScript');
// Outputs: JavaScript is the backbone of modern web development. JavaScript is powerful.

In the above code, the replace() method uses the regexPattern to replace all case-insensitive occurrences of “Javascript” with “JavaScript”. The ‘g’ flag makes the search global (across the entire text), and the ‘i’ flag makes it case-insensitive.

Form Validation with Regex

Finally, let’s discuss one of the most common uses of regex – form validation. For instance, validating email addresses is crucial for user sign-up forms. Regex can match the specific pattern that email addresses follow.

Let’s look at a simple example:

<!DOCTYPE html>
    <input type="email" id="email" placeholder="Enter your email">
    <button type="button" onclick="validateEmail()">Submit</button>
  function validateEmail() {
    let emailInput = document.getElementById("email").value;
    let emailRegex = /^[a-zA-Z0-9._-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,6}$/;

    if (emailRegex.test(emailInput)) {
      alert("Valid email!");
    } else {
      alert("Invalid email. Please enter a correct email address.");

In the above code, we created a simple HTML form with an email input field and a submit button. The validateEmail() function is called when the button is clicked. Inside the function, we use the test() method on our email regex pattern to check if the input matches the pattern. If it does, an alert indicates a valid email, and if not, an error message is shown.


Regex is a powerful tool in a developer’s arsenal, but it’s crucial to strike the right balance between complexity and readability. With practice, you’ll become proficient at using regex for a wide range of tasks, streamlining your code and enhancing your applications.

And that’s a wrap for Day 9! We’ve only just scratched the surface of regex, but by understanding the basic concepts and syntax, you’ll be well-equipped to start incorporating regex into your JavaScript projects. Stay tuned for more exciting tutorials as we continue our 30-day JavaScript adventure!

Next: 30 Days of JavaScript: Error Handling and Debugging — Day 10

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