string to number conversion in javascript

Question

I have a function having following lines:

payementReceived=data.toJSON().total;
paymentTotal=$("#paymentTotal").html();
console.log(typeof(parseInt(paymentTotal))); 
console.log(typeof(parseInt(paymentReceived)));
console.log(parseInt(paymentTotal)-parseInt(paymentReceived));

I get the following in console

number
number
NaN

i don't understand if both are numbers then why it isn't able to give the proper substraction result.

• Oded: new Number(), not just Number(). Or rather - parseInt(xxx, 10)
• Niklas: typeof(NaN) === "number"
• Bergi: Becaue the NaN value is of type number as well?
• Oded: What are the values of paymentTotal and paymentReceived?
• Basic: Note that when you use parseInt, you should always include 10 as a second parameter (otherwise numbers starting with a 0 will be read as base 8!)

Answer 1

The values are number in that their contents are a number, but it doesn't mean that the number is valid.

typeof NaN === 'number'

If you are getting a NaN back from your subtraction, one or both of your input values are invalid numbers.

Answer 2

problem is because of the undefined varaible used "paymentReceived" if you are sure that the result is a number you can always use parseInt

console.log(parseInt(paymentTotal)-parseInt(payementReceived));

Answer 3

Just a funny idea :

if (typeof n === "number" && n+1 !== n) {
 // this is a valid number
}

invalid+1 will still be invalid so it could check for invalid numbers.

Answer 4

try below code

console.log(Number(paymentTotal)-Number(payementReceived));