Coupon Code Validator | HTML, CSS & JavaScript

Coupon Code Validator with HTML, CSS & JavaScript

30 DAYS 30 PROJECT CHALLENGE

Day #17

Project Overview

A Coupon Code Validator built using HTML, CSS, and JavaScript that allows users to apply discount codes and see updated pricing instantly.
The project validates coupon inputs, applies percentage-based discounts, and provides clear feedback for valid or invalid codes, simulating real-world e-commerce behavior.

Key Features

Validates coupon codes entered by the user.
Applies percentage-based discounts dynamically.
Instantly updates the final price after applying a coupon.
Displays clear success and error messages.
Prevents empty or invalid coupon submissions.
Clean, responsive, and user-friendly interface.
Easy to extend with expiry dates or backend validation.

HTML Code

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8" />
  <meta name="viewport" content="width=device-width, initial-scale=1.0"/>
  <title>Coupon Code Validator</title>
  <link rel="stylesheet" href="style.css" />
</head>
<body>

  <div class="coupon-container">
    <h2>Apply Coupon</h2>

    <div class="price">
      Original Price: ₹<span id="originalPrice">1000</span>
    </div>

<p class="available">
  Available Coupons: <strong>SAVE10</strong>, <strong>SAVE20</strong>, <strong>DISCOUNT50</strong>
</p>

    <input
      type="text"
      id="couponInput"
      placeholder="Enter coupon code"
    />

    <button onclick="applyCoupon()">Apply Coupon</button>

    <p class="message" id="message"></p>

    <div class="final-price">
      Final Price: ₹<span id="finalPrice">1000</span>
    </div>
  </div>

  <script src="script.js"></script>
</body>
</html>

CSS Code

* {
  box-sizing: border-box;
  font-family: "Segoe UI", sans-serif;
}

body {
  min-height: 100vh;
  background: #042453;
  display: flex;
  justify-content: center;
  align-items: center;
}

.coupon-container {
  background: #ffffff;
  width: 320px;
  padding: 25px;
  border-radius: 12px;
  text-align: center;
  box-shadow: 0 15px 30px rgba(0,0,0,0.1);
}

h2 {
  margin-bottom: 15px;
}

.price,
.final-price {
  margin: 10px 0;
  font-weight: 600;
}

input {
  width: 100%;
  padding: 10px;
  border-radius: 6px;
  border: 1px solid #ccc;
  margin: 10px 0;
}

button {
  width: 100%;
  padding: 10px;
  border: none;
  border-radius: 6px;
  background: #4f46e5;
  color: white;
  cursor: pointer;
}

.message {
  margin-top: 10px;
  font-size: 14px;
}

Javascript Code

const originalPrice = 1000;
const finalPriceEl = document.getElementById("finalPrice");
const message = document.getElementById("message");

const coupons = {
  SAVE10: 10,
  SAVE20: 20,
  DISCOUNT50: 50
};

function applyCoupon() {
alert("Try these coupons: SAVE10, SAVE20, DISCOUNT50");
  const input = document.getElementById("couponInput").value.trim().toUpperCase();

  if (!input) {
    message.style.color = "red";
    message.innerText = "Please enter a coupon code";
    return;
  }

  if (coupons[input]) {
    const discount = coupons[input];
    const discountedPrice = originalPrice - (originalPrice * discount) / 100;

    finalPriceEl.innerText = discountedPrice;
    message.style.color = "green";
    message.innerText = `Coupon applied! You saved ${discount}%`;
  } else {
    finalPriceEl.innerText = originalPrice;
    message.style.color = "red";
    message.innerText = "Invalid coupon code";
  }
}