Example of chaining multiple promises

expenses.js

const monthlyRent = 600;
const monthlyFoodCosts = 420.5;
const monthlyElectricBill = 45;
const monthlyGymMemberShip = 38;
const monthlySpotifyMemberShip = 15;

let costsOutstanding = 1118.5;

const payExpense = (expenseAmount) => {
	return new Promise((resolve, reject) => {
		if (expenseAmount) {
			setTimeout(() => {
				costsOutstanding -= expenseAmount;
				console.log('Paid! outstanding is: ' + costsOutstanding);
				resolve();
			}, 500);
		} else {
			reject('Sorry! Your payment did not go through');
		}
	});
};

const checkIfPaidEverything = () => {
	if (costsOutstanding > 0) {
		console.log('You still have ' + calculatedTotal + ' to pay!');
	} else {
		console.log('Everything is paid! Woohoo!');
	}
};

// Pay one after the other
payExpense(monthlyRent)
	.then(() => {return monthlyFoodCosts;})
	.then(payExpense)
	.then(() => {return monthlyElectricBill;})
	.then(payExpense)
	.then(() => {return monthlyGymMemberShip;})
	.then(payExpense)
	.then(() => {return monthlySpotifyMemberShip;})
	.then(payExpense)
	.then(checkIfPaidEverything)
	.catch((message) => {
		console.log(message);
	});