[REFACTOR] Duplicate coupon logic implemented independently in app.js and js/coupon-validator.js

[munazzaghazali7-hash]

🧩 Current Code Situation

The coupon system (CARA20: 20% off, WELCOME10: 10% off) is implemented twice, independently, in two separate files:

• app.js — used on cart.html, bound to #apply-coupon-btn / #coupon-code
• js/coupon-validator.js — used on checkout.html, bound to #applyCouponBtn / #couponCodeInput

Both hardcode the same coupon codes and discount percentages separately. There is no shared source of truth. If a coupon is added, removed, or its discount percentage changes, both files must be updated in sync manually — miss one and cart.html/checkout.html will silently disagree on what a coupon is worth.

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🧠 Reason for Refactor

Extract the coupon codes/percentages into a single shared file, js/coupon-config.js, exposing window.CARA_COUPONS. Update both app.js and js/coupon-validator.js to read from this shared object instead of maintaining their own hardcoded copies. Load the new config script before both consumers on cart.html and checkout.html.

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🚧 Proposed Refactor Plan

Not a live user-facing bug — both implementations currently work correctly on their respective pages. This is a maintainability/consistency risk: future coupon changes require remembering to update two unrelated files.

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✅ Checklist

• I have identified the part of the code that needs refactoring.
• I have ensured no functionality will be broken.
• I have tested similar code paths before.