How can I check if x is an integer in javascript?

Question

1 -> OK
11 -> OK
1.1 -> not OK (decimal place)
null -> not OK (null)
a -> not OK (letter)
1e1 -> not OK (letter)

1 1 -> not OK (sapce in any position (include front or end))

var x = document.forms["myForm"]["numofquestions"].value;    

if (x==null || x=="" || isNaN(x) || x<1 || x>500 || (x%1 != 0)) {
   alert("Please fill in number between 1 - 1000");
}

This post might help you: http://stackoverflow.com/questions/1323314/how-to-detect-if-a-given-number-is-an-integer — Ryan Fung, Jun 04 '14 at 02:08

score 0 · Answer 1 · answered Jun 04 '14 at 02:09

0

You could convert your value to an integer and check if this number is equal to your value:

parseInt(n) === n;

answered Jun 04 '14 at 02:09

yckart

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@undefined No, why should it fail? A string gets converted to a number (or NaN), and if this doesn't match to the input-value it will be falsy and everything is ok... – yckart Jun 04 '14 at 02:21
I had removed my comment, but I repeat it, this won't work. `parseInt('1')` is not strictly equal to `'1'`. – Ram Jun 04 '14 at 02:24
@undefined: Which is OK, isn't it? `'1'` is not an integer, it's a string. – Felix Kling Jun 04 '14 at 02:50
@FelixKling Well, `x` in the question refers to a form input's value, which is a string. OP is validating user inputs. – Ram Jun 04 '14 at 03:02

score 0 · Answer 2 · answered Jun 04 '14 at 02:11

0

to check you can use

n % 1 === 0

answered Jun 04 '14 at 02:11

aljgom

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How can I check if x is an integer in javascript?

2 Answers2