Completed cash register, but need some explanation


My code..

function StaffMember(name,discountPercent){ = 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 = {
    "lastTransactionAmount": 0,
    "add": function(itemCost){ += (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.lastTransactionAmount;
        this.lastTransactionAmount = 0;
    // Create a new method applyStaffDiscount here
    { -= * (employee.discountPercent / 100);

// Apply your staff discount by passing the 'me' object 
// to applyStaffDiscount

// Show the total bill
console.log('Your bill is ';

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




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


google search
javascript variable default value


As the is a number Value
In javascript you will then have a whole set of Methods ( predefined functions )
which can be found under the
=google search=> javascript number.prototype
look in the left-hand-column


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


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.