Completed cash register, but need some explanation


#1

https://www.codecademy.com/courses/close-the-super-makert/0/7?curriculum_id=506324b3a7dffd00020bf661#

My code..

function StaffMember(name,discountPercent){
    this.name = name;
    this.discountPercent = discountPercent;
}

var sally = new StaffMember("Sally",5);
var bob = new StaffMember("Bob",10);

// Create yourself again as 'me' with a staff discount of 20%
var me=new StaffMember("ezio",20);

var cashRegister = {
    "total":0,
    "lastTransactionAmount": 0,
    "add": function(itemCost){
        this.total += (itemCost || 0);
        this.lastTransactionAmount = itemCost;
    },
    "scan": function(item,quantity){
        switch (item){
        case "eggs": this.add(0.98 * quantity); break;
        case "milk": this.add(1.23 * quantity); break;
        case "magazine": this.add(4.99 * quantity); break;
        case "chocolate": this.add(0.45 * quantity); break;
        }
        return true;
    },
    "voidLastTransaction" : function(){
        this.total -= this.lastTransactionAmount;
        this.lastTransactionAmount = 0;
    },
    // Create a new method applyStaffDiscount here
    "applyStaffDiscount":function(employee)
    {
        this.total -= this.total * (employee.discountPercent / 100);
}
};

cashRegister.scan('eggs',1);
cashRegister.scan('milk',1);
cashRegister.scan('magazine',3);
// Apply your staff discount by passing the 'me' object 
// to applyStaffDiscount
cashRegister.applyStaffDiscount(me);

// Show the total bill
console.log('Your bill is '+cashRegister.total.toFixed(2));

1- There are some things that I don't understand. Why are we using return true; and what does it do?
2- What does this.total += (itemCost || 0); mean? And why are we using it?(note that previously, we used this.total += itemCost; )
3- What is toFixed ? Why are we using it?


#2

@avil172,

1

Normally the switch()-Method has a =default:=-case,
and to make sure that the scan-method
if not ending by a break
it return's with a Boolean true

2

google search
javascript variable default value site:stackoverflow.com
=> http://stackoverflow.com/questions/16696642/setting-a-default-variable-value-in-a-function
==> http://stackoverflow.com/questions/476436/is-there-a-null-coalescing-operator-in-javascript/476445#476445

3

As the cashRegister.total is a number Value
In javascript you will then have a whole set of Methods ( predefined functions )
which can be found under the
number.prototyoe
=google search=> javascript number.prototype site:developer.mozilla.org
= https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number/prototype
look in the left-hand-column


#3

1- so, i take it that return is a placeholder for default? or, it is the default itself?


#4

He's saying you need a "default:" case to take any arguments that didn't happen in the switch. So after your last case case "chocolate": add a default to the switch.

case "chocolate": this.add(0.45 * quantity); break;
default: break;
}

There are several issues with your code other than just that however. But @leonhard_wettengmx_n has covered those in his above post.