This code killing me


#1

what is wrong with this code?
I alwause get error false!

var cashRegister = {
        total:0,
        //Dont forget to add your property
        add: function(itemCost) {
            this.total +=  itemCost;
            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;
        },
        //Add the voidLastTransaction Method here
        voidLastTransaction: function(total, lastTransactionAmount) {
            return total - lastTransactionAmount; 
        }
    };

cashRegister.scan('eggs',1);
cashRegister.scan('milk',1);
cashRegister.scan('magazine',1);
cashRegister.scan('chocolate',4);

//Void the last transaction and then add 3 instead
cashRegister.voidLastTransaction();
cashRegister.scan('chocolate',3);






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

#2

It isn't necessary to have parameters for your voidLastTransaction function. Also, you need to return with a "-=" instead of just "-".

Should look like this:
voidLastTransaction: function() {
this.total -= this.lastTransactionAmount;
}