postage_calculator.js

function postage(order) {
    if(order.location === 'UK') {
        if (totalPrice(order) >= 100) {
            return 0;
        }

        if (totalWeight(order) < 1) {
            return 2.99;
        }

        if (totalWeight(order) >= 1 && totalWeight(order) < 3) {
            return 4.99;
        }

        if (totalWeight(order) >= 3) {
            return 6.99
        }
    }

    if(order.location === 'EU') {
        if (totalWeight(order) < 1) {
            return 4.99;
        }

        if (totalWeight(order) >= 1 && totalWeight(order) < 3) {
            return 6.99;
        }

        if (totalWeight(order) >= 3) {
            return 8.99
        }
    }
}