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Identifying data types

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Nov 02.2008

Hi all,

I’m currently working on a simple javascript programme and have hit a brick wall (surprise surprise…).

I need my programme to recognise when the user enters a non-numeric number, ie a word or even just gibberish. At the moment I am trying this conditional:

if (typeof(age_of_user) != Number) {
alert(‘Error. Please enter your age in numeric form.’);
}

This alert message appears no matter what the user has entered in the text box, leading me to suspect something has gone awry. Any clues?

Thanks folk,

Mike

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JavaScript

6 Comments(s) ↴

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@Declan1991Nov 02.2008 — if (typeof age_of_user != "number") {
alert('Error. Please enter your age in numeric form.');
}
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@MrNobodyNov 02.2008 — Actually, I don't think even the above will work. All [B]form[/B] and prompted user input is always in string format. Thus, the [B]typeof[/B] operator will never return "number" for those types of values even if they are purely numbers. The solution is to use other methods of validation -- [B]Regular Expression[/B]s or the [B]Number()[/B] object itself.
var num = Number(age_of_user);
if (isNaN(num)) {
alert('Error. Please enter your age in numeric form.');
}
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@Declan1991Nov 02.2008 — Ya, MrNobody is right, it has to be converted to a number first, I presumed you did that. However, isNaN can take string as an input, so you actually don't need to convert for MrNobody's, while you do for mine.
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@MrNobodyNov 02.2008 — What he meant by that is that you can do this:
[CODE]if (isNaN(age_of_user)) {
alert('Error. Please enter your age in numeric form.');
}[/CODE]
But I was just being explicit -- for teaching purposes.
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@javascriptloverauthorNov 02.2008 — That's really interesting about form content being treated as a string Mr Nobody, thankyou very much.
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@rnd_meNov 03.2008 — [CODE]var x = "5"
Number(x) == x // true


var x = "five"
Number(x) == x // false[/CODE]
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