Checkout System (Backend)

Pre-requisites: Nodejs v8.1.2 Install dependencies: npm install Run tests: npm run test

Problem

• To implement a checkout system that calculates the total of all items by applying any customer specific pricing rules (i.e. discounts). The checkout interface looks like:

const checkout = new Checkout(...);
checkout.add(itemId);
checkout.add(itemId);
checkout.total();

Assumptions

• All product and discount prices are stored in cents to avoid rounding issues. These could be easily be formatted to dollars as required. Another option could have been to use a library like big.js or decimal.js for pricing and calculations, but avoided for now.

Design Notes

• Full async API to support the lookup of products and price rules from an external store (e.g. database) instead of just hardcoded values.

• Pricing rules are applied in the form of adjustments which can be at the product level or the entire checkout level (e.g. 10% off if total price > $1000). In addition, all adjustments are made available to subsequent rules via pricingContext. This allows for more advanced scenarios if a rule needs to check whether an adjustment has already been applied.

• The use of _ infront of attributes and functions implies a 'private' member.