ES6-Handson/js/main.js

class Mortgage {
  constructor(principal, years, rate) {
    this.principal = principal;
    this.years = years;
    this.rate = rate;
  }

  get monthlyPayment() {
    let monthlyRate = this.rate / 100 / 12;
    return this.principal * monthlyRate / (1 - (Math.pow(1/(1 + monthlyRate),
                    this.years * 12)));
  }

  get amortization() {
    let monthlyPayment = this.monthlyPayment;
    let monthlyRate = this.rate / 100 / 12;
    let balance = this.principal;
    let amortization = [];
    for (let y=0; y<this.years; y++) {
        let interestY = 0;
        let principalY = 0;
      for (let m=0; m<12; m++) {
              let interestM = balance * monthlyRate;
              let principalM = monthlyPayment - interestM;
              interestY = interestY + interestM;
              principalY = principalY + principalM;
              balance = balance - principalM;
      }
      amortization.push({principalY, interestY, balance});
    }
    return amortization;
  }
}



document.getElementById('calcBtn').addEventListener('click', () => {
    let principal = document.getElementById("principal").value;
    let years = document.getElementById("years").value;
    let rate = document.getElementById("rate").value;
    let mortgage = new Mortgage(principal, years, rate);
    document.getElementById("monthlyPayment").innerHTML = mortgage.monthlyPayment.toFixed(2);
    document.getElementById("monthlyRate").innerHTML = (rate / 12).toFixed(2);
    let html = "";
    mortgage.amortization.forEach((year, index) => html += `
        <tr>
            <td>${index + 1}</td>
            <td class="currency">${Math.round(year.principalY)}</td>
            <td class="stretch">
                <div class="flex">
                    <div class="bar principal"
                         style="flex:${year.principalY};-webkit-flex:${year.principalY}">
                    </div>
                    <div class="bar interest"
                         style="flex:${year.interestY};-webkit-flex:${year.interestY}">
                    </div>
                </div>
            </td>
            <td class="currency left">${Math.round(year.interestY)}</td>
            <td class="currency">${Math.round(year.balance)}</td>
        </tr>
    `);
    document.getElementById("amortization").innerHTML = html;

});