Why does the lastTransactionAmount have to be set to 0?


#1


I dont understand why it is necessary to set my lastTransactionAmount to 0 when if I call the scan function again and I plug in a new item cost it will just erase the old value of lastTransactionAmount and put in the new one.

the only reason I think that it erases it is because in the add function if i just set the this.total to this.total = itemCost I am assuming that the previous this.total will be erased by the newly called itemCost

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

};

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);


Replace this line with your code.


#2

So if there is a subsequent call to the method no further change can occur. We can only void a transaction once.


#3

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