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JavaScript Object-Oriented JavaScript (2015) Introduction to Methods Finishing the Calculator

Courses Plus Student 8,447 Points

Finish the calculator

Hi guys, in the final challenge of the Object oriented javaScript lesson, we were asked to finish a calculator app. We had to do the subtract, multiply and divide part. I tried out the app in my text editor and I kept getting all the wrong answers. like 50 * 5 would equal 0 or 5 * 25 would equal 2500. However, in the code challenge it was saying the answers are correct. Here's the app

var calculator = {
  sum: 0,
  add: function(value) {
    this.sum += value;
  subtract: function(value) {
    this.sum -= value;
  multiply: function(value) {
  this.sum *= value;
  divide: function(value) {
  this.sum /= value;
  clear: function() {
    this.sum = 0;
  equals: function() {
    return this.sum;

Video link: https://teamtreehouse.com/library/objectoriented-javascript/introduction-to-methods/finishing-the-calculator

What's going on? Is the code correct?

1 Answer

Kevin Becerra
Kevin Becerra
14,243 Points

The app is working fine but since the way it was structured has you start at 0 and always sum equal a certain number it may be confusing to use. If you wanted to multiply 50 by 5 you had to make sure you first cleared the calculator and then added the 50 or 5, then you call the multiply function. Even there you would then have to remember you cleared it and so on. Whats adds on to it not being the best is that each time you called the functions you always get an undefined object which really doesn't allow you to know what the current sum is in between all the math you are trying to do.

Hope this helps!