decouple_temporal_coupling.js

const events = require('events');
const emitter = new events.EventEmitter();

emitter.on('purchased', function(user, total) {
    if (total >= 1000) {
        giveCoupon(cart.user, total);
    }
});
emitter.on('purchased', function(user, total) {
    if (ok && total >= 5000) {
        lottery(cart.user, total);
    }
});

function purchase(cart) {
    const total = 0;
    for (let item of cart.items) {
        total += item.price;
    }
    const ok = payByCreditCard(cart.user, total);
    if (ok) {
        emitter.emit('purchased', cart.user, total);
    }
    return ok;
}