value is a number

[Jeff Thies]

I'm trying to test if a value is a number.

I thought I could do this:

var test='not_a_num ber';
var test2='4.00';

num_test=parseF loat(test);

if(num_test == 'NaN'){alert('t hat was not a number')}

But that doesn't work. (at least not in NS)

Maybe a regex?

Jeff

[Douglas Crockford]

Re: value is a number

> I'm trying to test if a value is a number.[color=blue]
>
> I thought I could do this:
>
> var test='not_a_num ber';
> var test2='4.00';
>
> num_test=parseF loat(test);
>
> if(num_test == 'NaN'){alert('t hat was not a number')}
>
> But that doesn't work. (at least not in NS)
>
> Maybe a regex?[/color]

Use the isNaN() function, or better, use the isFinite() function.

if (!isFinite(test )) {alert(test + ' is not a number');}

NaN is a freaky thing. The comparison operators don't work with it.

http://www.crockford.com/javascript/survey.html

[Dr John Stockton]

Re: value is a number

JRS: In article <QXrub.6092$Rk5 .4193@newsread1 .news.atl.earth link.net>,
seen in news:comp.lang. javascript, Jeff Thies <nospam@nospam. net> posted
at Tue, 18 Nov 2003 16:40:16 :-[color=blue]
> I'm trying to test if a value is a number.
>
> I thought I could do this:
>
>var test='not_a_num ber';
>var test2='4.00';
>
>num_test=parse Float(test);
>
>if(num_test == 'NaN'){alert('t hat was not a number')}
>
> But that doesn't work. (at least not in NS)[/color]

NaN is not a number; since this might occur in many ways, it is equal to
nothing, not even itself. But 'NaN' is a perfectly good non-numeric
string, and +'NaN' gives NaN without being equal to it.

[color=blue]
>Maybe a regex?[/color]

Yes. In any reasonable application in which it is right to validate a
number, it is likely that the set of suitable numbers is much smaller
than the set of possible numbers. Likewise formats.

You may in practice want non-negative integers, with no need to allow
the format 1e2; in that case test with RegExp /^\d+$/ - see
<URL:http://www.merlyn.demo n.co.uk/js-maths.htm#Valid >.

Once the format is OK, you can convert the string to a number in safety
with unary +
Numeric = +Stringy.value
and then if necessary do further tests with arithmetic comparison.

E.G. : In US notation, seconds format is RegExp /^[0-5]\d$/ = 00..59 but
there is nothing quite so simple for hours 01..12 ; /^0[1-9]|1[0-2]$/ .

--
© John Stockton, Surrey, UK. ?@merlyn.demon. co.uk Turnpike v4.00 IE 4 ©
<URL:http://jibbering.com/faq/> Jim Ley's FAQ for news:comp.lang. javascript
<URL:http://www.merlyn.demo n.co.uk/js-index.htm> JS maths, dates, sources.
<URL:http://www.merlyn.demo n.co.uk/> TP/BP/Delphi/JS/&c., FAQ topics, links.