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Experiment 2: Use JavaScript to validate forms

This experiment demonstrates how to implement client-side form validation using JavaScript.

Overview

In this experiment, we enhanced a basic login form with JavaScript validation to:

Implementation

The implementation consists of three main files:

JavaScript Code (script.js)

document.addEventListener("DOMContentLoaded", function () {
    const form = document.querySelector("form");

    form.addEventListener("submit", function (event) {
        event.preventDefault(); 

        const email = form.email.value.trim();
        const password = form.password.value.trim();
        let isValid = true;
        
        if (email === "") {
            alert("Email is required.");
            isValid = false;
        }

        else if (!validateEmail(email)) {
           alert("Please enter a valid email address.");
            isValid = false;
        }

        if (password === "") {
            alert("Password is required.");
            isValid = false;
        }

        else if (password.length < 6) {
            alert("Password must be at least 6 characters long.");
            isValid = false;
        }

        
        if (isValid) {
            alert("Login successful!");
            form.submit();
        }
    });

    function validateEmail(email) {
        const emailPattern = /^[^\s@]+@[^\s@]+\.[^\s@]+$/;
        return emailPattern.test(email);
    }
});

HTML Code (index.html)

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Login Page</title>
    <link rel="stylesheet" href="styles.css">
</head>
<body>
    <div class="login-container">
        <h2>Login</h2>
        <form>
            <div class="form-group">
                <label for="email">Email</label>
                <input  type="email" name="email" required >
            </div>
            <div class="form-group">
                <label for="password">Password</label>
                <input type="password" id="password" name="password" required>
            </div>
            <button type="submit" class="login-button">Login</button>
        </form>
    </div>
    <script src="script.js"></script>
</body>
</html>

CSS Code (styles.css)

body {
    font-family: Arial, sans-serif;
    background-color: #f4f4f4;
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
    margin: 0;
}
.login-container {
    background: #fff;
    padding: 20px;
    border-radius: 8px;
    box-shadow: 0 4px 6px rgba(0, 0, 0, 0.1);
    width: 300px;
}   
.login-container h2 {
    margin-bottom: 20px;
    text-align: center;
}
.form-group {
    margin-bottom: 15px;
}
.form-group label {
    display: block;
    font-size: 14px;
    margin-bottom: 5px;
}
.form-group input {
    width: 100%;
    padding: 10px;
    border: 1px solid #ccc;
    border-radius: 4px;
    box-sizing: border-box;
}
.login-button {
    width: 100%;
    padding: 10px;
    background-color: #007BFF;
    color: white;
    border: none;
    border-radius: 4px;
    cursor: pointer;
}
.login-button:hover {
    background-color: #0056b3;
}

Preview

The form looks similar to Experiment 1 but includes validation feedback when users attempt to submit invalid data.

View Implementation

👉 See the live implementation of this form validation example.

Exp-1 Exp-2 Exp-3