(Number(value) !== NaN) always true

Question

I am using typescript for the first time, and I face a quite strange problem.

I am trying to make calculation like a calculator, so when a user press a button it could be a digit, 2 3 4 ... or an operation * \ + ...

On button press, I call a function, and the function check if it is a digit, or an operation in order to call the adequate function.

I compare my string like this :

if (Number(value) !== NaN) {
  // it is a number
} else {
  // it is an operation
}

although this work in the console ( by that I mean I do have a digit (3,4,5) when I press a number and NaN when I press an operation) this line ALWAYS return true, so I always consider it a number.

What am I doing wrong here?

thanks

See: https://stackoverflow.com/questions/34261938/what-is-the-difference-between-nan-nan-and-nan-nan — roryrjb, Sep 23 '18 at 06:13

score 3 · Accepted Answer · answered Sep 23 '18 at 06:13

3

To check is value is NaN or not you should use isNaN function.

if(isNaN(value)) {
  //do this if NaN
} else {
  //do this if not
}

BTW: On SO a lot of similar questions ;) eg: How do you test for NaN in JavaScript?

answered Sep 23 '18 at 06:13

Alex Shtromberg

740
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21

thougt typescript would have a different function – Bobby Sep 23 '18 at 06:14
"*BTW: On SO a lot of similar questions*" - please flag to close as a duplicate, then. – Bergi Sep 23 '18 at 08:31

score 0 · Answer 2 · answered Sep 23 '18 at 06:12

0

Use isNaN(value). It returns true if value is a number and False otherwise.

answered Sep 23 '18 at 06:12

Mean Coder

304
1
12

(Number(value) !== NaN) always true

2 Answers2