JavaScript Arithmetic's

Question

I am wondering this code, trying to understand the nan or Nan value since it is not falsy or truthy and it's just a Number object of the type of number, the question is here why does this return zero since Nan is not falsy

my expected value here is Nan

    tip = '.'
    total = 10
    let totalPlusTip = ((total * (tip/100)) + total) || 0
    console.log(totalPlusTip) //0

my expected value here is 110

    tip = 10
    total = 100
    let totalPlusTip = ((total * (tip/100)) + total) || 0
    console.log(totalPlusTip) //110

since Nan is not false why isn't returning Nan when we do

`since Nan is not falsy` But it **is** [falsy](https://developer.mozilla.org/en-US/docs/Glossary/Falsy) — Nicholas Tower, Jan 08 '22 at 15:32
Really can you please point me to documentation on that if available so I can understand further — Swiss bobo, Jan 08 '22 at 15:33
Here you are: https://developer.mozilla.org/en-US/docs/Glossary/Falsy — Nicholas Tower, Jan 08 '22 at 15:33
Thank you very much, i searched for this on google, all i saw was Nan is not falsy, but your comment has been very helpful. and yes Nan is truly falsy — Swiss bobo, Jan 08 '22 at 15:35
You could also do `!!NaN` in your browser console to see that it evaluates to `false` — phuzi, Jan 08 '22 at 15:47

score 1 · Answer 1 · answered Jan 08 '22 at 15:55

The reason why the first code output 0 is because NaN is false and in || operator, the Logical OR operator || returns the value of its second operand, if the first one is false.

You could see below, the value of ((total * (tip/100)) + total) is NaN and !NaN return true which means is return false. Since NaN is false, || return the second value which is 0.

  let tip = '.'
   let total = 10
    let totalPlusTip = ((total * (tip/100)) + total) || 0
  console.log(total * (tip/100))
  console.log(!NaN)
    console.log(totalPlusTip) //0

Thank you, my confusion was i thought Nan isn't falsy but now i get the whole scope — Swiss bobo, Jan 08 '22 at 19:06

score 0 · Answer 2 · answered Jan 08 '22 at 15:43

0

Unfortunately, It's falsy.

However, you can use Nullish coalescing operator (??) if you don't care about IE.

let totalPlusTip = ((total * (tip/100)) + total) ?? 0

Only null or undefined will be 0.

answered Jan 08 '22 at 15:43

Hao-Jung Hsieh

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alright thanks the problem was my mis understanding of the Nan value , its also falsy – Swiss bobo Jan 08 '22 at 19:07

JavaScript Arithmetic's

2 Answers2