Playing around with ES6, classes, and testing with Chai and Mocha

expenseTrackerChaiES6.js

const l = console.log;

chai.should();
mocha.setup('bdd');

// Pre-config ⇡⇡⇡⇡⇡

class MoneyTracker {
  constructor() {
    this.income = [];
    this.expenses = [];
  }
  addExpense(name, amount) {
    this.expenses.push({[name] : amount})
    return this.expenses.slice();
  }
  addIncome(name, amount) {
    this.income.push({[name] : amount})
    return this.income.slice();
  }
  sumExpenses() {
  	let sum = 0;
   	this.expenses.map(expense => {
    	sum += expense[Object.keys(expense)[0]];
    })
    return sum;
  }
  sumIncome() {
  	let sum = 0;
   	this.income.map(income => {
    	sum += income[Object.keys(income)[0]];
    })
    return sum;
  }
  getDaysUntilSalary(date) {
  	let daysOfThisMonth = (new Date((new Date()).getFullYear(), (new Date()).getMonth()+1, 0)).getDate();
    let dateToday = date && date.getDate() || new Date().getDate();
    return daysOfThisMonth - dateToday + 16;
  }
  getDailyAllowance() {
		return (this.sumIncome() - this.sumExpenses()) / this.getDaysUntilSalary();
	}
}

let myTracker = new MoneyTracker();
myTracker.addIncome('salary', 1000);
myTracker.addExpense('rent', 330);
l(myTracker.getDailyAllowance());

l(document.querySelector('#allowance').innerText += myTracker.getDailyAllowance());

let assert = chai.assert;

describe('Budget tracker', () => {
	it('should return 8700 after adding 29 items for "300" when running "sumExpenses()"', () => {
  	let testTracker = new MoneyTracker();
    Array(29).fill().forEach(() => {
    	testTracker.addExpense('banana', 300);
    })
    assert.equal(testTracker.sumExpenses(), 8700);
  });
  it('should return "30" when running "getDaysUntilSalary()" on 17th of March 2018', () => {
  	let testTracker = new MoneyTracker();
   	let daysUntilSalary = testTracker.getDaysUntilSalary(new Date(2018, 4, 17))
    assert.equal(daysUntilSalary, 30);
  });
  it('should return "3300" when running "sumIncome()" after adding 11 items into income', () => {
  	let testTracker = new MoneyTracker();
    [...Array(11)].forEach(() => {
    	testTracker.addIncome('banana', 300);
    })
    assert.equal(testTracker.sumIncome(), 3300);
  })
});

let testResults = mocha.run();