How to use If Else for check validation is number in Javascript

Question

This is my code

else if(form.txtPrice.IsNumber){
    alert("Price must be number") form.txtPrice.focus();
    return false;

I can not check validation must be number in Javascript, everybody help me please, thank you so much!

Please [format](https://stackoverflow.com/help/formatting) your question, and have a look at [How do I ask a good question?](https://stackoverflow.com/help/how-to-ask) — Andreas, Mar 29 '19 at 12:20
@Keith you shouldnt provide answers in comments, it circumvents the voting process which helps determine good/bad/safe/unsafe answers — Marie, Mar 29 '19 at 14:05

score 0 · Answer 1 · answered Mar 29 '19 at 13:44

0

Use isNaN(value).

This returns true if the value is not a number. If the value is a number, will return false.

answered Mar 29 '19 at 13:44

lok30

score 0 · Answer 2 · answered Mar 29 '19 at 13:57

0

Using only isNaN is risky, it has some big inconvenient; These strings will be considered valid numbers:

you could do more:

function isNumber(input) {
  return typeof input === "number" && !isNaN(input);
}

note that you have to parse if before if you have a string (parseInt/parseFloat)

answered Mar 29 '19 at 13:57

Apolo

1

To be fair, they are valid numbers just in different and unexpected formats – Marie Mar 29 '19 at 14:03
`typeof Infinity , 1e355 , 0xf` are all `number` There is `Number.isFinite` is you want to prevent those. – Keith Mar 29 '19 at 14:25
I'm talking about user input strings, for eg. `input = "Infinity";` which is valid number according to `isNaN`. This should disable implicit parsing. Furthermore, `parseInt('Infinity')` returns NaN, which is good IMO – Apolo Apr 01 '19 at 12:33
I still agree they are valid numbers, just not the format you want your users to send – Apolo Apr 01 '19 at 12:34

2 Answers2