JavaScript-Pass values between objects

Question

when I enter at the prompt 0, than I am expecting an alert "stop" but receive "go" instead. Can you help me to get the alert "stop"?

var toyota = {
 make: "Toyota",
 model: "Corolla",
 fuel: 0,
 tank: function(addingfuel) {
 this.fuel = this.fuel + addingfuel;
 },
 start: function() {
 if (this.fuel === 0) {
 alert("stop");
 } else {
 alert("go");
 }
 },
};
var addingfuel = prompt("Please enter fuel added", "liter");
toyota.tank();
toyota.start();

• mplungjan: Prompt returns a string. 1, convert to number: +addingfuel; 2. pass it toyota.tank(+addingfuel);
• James: The var addingFuel is completely separate from the parameter function(addingFuel). Two completely separate unrelated variables that happen to have the same name.

Answer 1

It will work fine if you change this code

this.fuel = this.fuel + addingfuel;

to

 this.fuel = this.fuel + (addingfuel || 0);

Answer 2

You need to change your code a little bit

var toyota = {
 make: "Toyota",
 model: "Corolla",
 fuel: 0,
 tank: function(addingfuel) {
 this.fuel = this.fuel + (addingfuel || 0);
 },
 start: function() {
 if (this.fuel === 0) {
 alert("stop");
 } else {
 alert("go");
 }
 },
};

Explanation When you pass nothing while calling toyota.tank() this will take argument as undefined and append undefined with a number will give you NaN

0 + undefined

Answer 3

window. prompt returns string type as a return value. That is why when you adding fuel (number) to addingfuel (string) it results "00" and your condition fails.

In order to overcome this issue, you should cast string to number before working with that value.

tank: function(addingfuel) {
 var numberValue = parseFloat(addingfuel, 10);
 numberValue = isNaN(numberValue) ? 0 : numberValue
 this.fuel = this.fuel + numberValue;
}

• Mister Jojo: this.fuel += numberValue; ;)
• doniyor2109: @MrJ Yea, that is better. Thanks

Answer 4

You've to pass the addingfuel with your tank(addingfuel) function other wise addingfuel contains undefined so finally it will show the go instead of stop.

N.B the value of addingfuel is string so you've to cast it to integer like this parseInt(addingfuel) otherwise your this.fuel === 0 condition will fail

Let try this way,

var toyota = {
 make: "Toyota",
 model: "Corolla",
 fuel: 0,
 tank: function(addingfuel) {
 this.fuel = this.fuel + parseInt(addingfuel);
 },
 start: function() {
 if (this.fuel === 0) {
 alert("stop");
 } else {
 alert("go");
 }
 },
};
var addingfuel = prompt("Please enter fuel added", "liter");
toyota.tank(addingfuel); // you need to pass this otherwise it is undefined
toyota.start();