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

Mike Ulvila
Mike Ulvila
16,268 Points
Posted by Mike Ulvila
Mike Ulvila
16,268 Points

Task 2 of 3: Implement the multiply method.

Will someone please help me with the code for the multiply method. I keep getting errors and can't figure it out. Thanks

Daniel Powell
Daniel Powell
23,321 Points

Please post the code you have tried so far.

Mike Ulvila
Mike Ulvila
16,268 Points
Mike Ulvila
Mike Ulvila
16,268 Points

this is one of many i've tried. i know it's not right because it would be passing the same number as the value. var calculator = { sum: 0, add: function(value) { this.sum += value; }, subtract: function(value) { this.sum -= value; }, multiply: function(value) { this.sum = this.add(value) * value; },

2 Answers

Daniel Powell
Daniel Powell
23,321 Points

You appear to be making the task more complicated than it needs to be.

Try to keep it simple:

function(value) {
    this.sum *= value
}

You can do the same thing with the '/=' operator as well.

If you want to make it more verbose, you could do:

function(value) {
    this.sum = (this.sum * value)
}
Mike Ulvila
Mike Ulvila
16,268 Points
Mike Ulvila
Mike Ulvila
16,268 Points

Ok, thank you, that works. I guess in my mind I was thinking since the sum = 0, no matter what value you put it it's going to return 0 right???

Daniel Powell
Daniel Powell
23,321 Points

You can't assume the sum will always be equal to 0. It could very well end up holding a running total that will be updated many times. In that case, your original formula could produce incorrect results.

By keeping the multiply function's code very narrow in functionality you end up programming defensively against possible future errors. And that's always a good thing.

I also edited my answer to include another example if you want to see the non-shorthand code.

Mike Ulvila
Mike Ulvila
16,268 Points
Mike Ulvila
Mike Ulvila
16,268 Points

Ok, thanks again for your help!

Cosimo Scarpa
Cosimo Scarpa
14,047 Points
Cosimo Scarpa
Cosimo Scarpa
14,047 Points

The result need to be something like this

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