JavaScript function to validate an integer value

Question

I'm building a shopping cart and I would like to use a JavaScript function to validate user input when entering the quantity value in the quantity text input. I would like to allow the entering of integer values only (no floats, no other characters).

I know that I can apply this function using onKeyUp event and also I found isNaN() function, but it returns true even for floats (which is not ok).

Can you guys help me out with this one?

Thanks.

there is a nice jQuery plugin for this: digitalbush.com/projects/masked-input-plugin — meo
– meo, Commented Jun 6, 2010 at 20:11
Don't forget to validate on the server side, too. It's very easy to stop JavaScript outputting 'irritating' messages like “Hey you! You're supposed to only input numbers here!”. — Marcel Korpel
– Marcel Korpel, Commented Jun 6, 2010 at 21:03

Vic · Accepted Answer · 2010-06-06 20:11:34Z

6

You can always check with parseInt:

if (number == parseInt(number))

answered Jun 6, 2010 at 20:11

Vic

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3 Comments

Marcel Korpel Over a year ago

OR'ing a value with 0 is faster: if (number == (number | 0)).

robocat Over a year ago

BEWARE: both answers above will return true for the strings '0x10' and '10.000000', '00000', '-0', and '+0'. Virtually always parseInt should be passed 10 as the second parameter to force it to use base 10 ie. parseInt(number,10). |0 is probably no faster if passed a string.

robocat Over a year ago

BEWARE: also the string '0e-400' returns true for both given solutions... and there are probably other corner cases (maybe near +/-MaxInt). Validating integers is hard in Javascript :)

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