prevent user from writing letter in textbox

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hi all ,
i want to make function in javascript which can prevent user from writing letters in textbox only allow number
i found this one

JavaScript

function prevent_number(event)
   {
       var charcode = (event.which) ? event.which : event.keycode
       if (charcode >31 &&(charcode<48||charcode >57))
        {


            alert('please enter only number ');
            return false;

       }
       else
        {


           return true ;

       }





   }

i want to know why he said charcode>31 &&(charcode<48||charcode>57)
the numbers from 0 to 9 their code is just from 48 to 57

Posted 5-Apr-14 22:42pm

fady_hasnaa

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2 solutions

Solution 1

Character code here represents the ASCII value of the character.
If you go through the character table at Ascii Table[^], you will get an idea why only these characters ranges are useful to you.

Posted 5-Apr-14 22:51pm

Abhinav S

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Peter Leow · Accepted Answer · 2014-04-06T03:26:00

Solution 2

charcode >31

is redundant, the following will do:

if (charcode<48 || charcode >57)

Posted 6-Apr-14 3:26am

Peter Leow

Updated 6-Apr-14 3:27am

v2

Comments

fady_hasnaa 7-Apr-14 1:02am

so what if i write
if (charcode>57)
?

Peter Leow 7-Apr-14 1:07am

You would have omitted checking of such characters like space, +, - etc. Look at the ASCII table provided by Abhinav S in this solution.

Peter Leow 7-Apr-14 3:26am

I have done my part in answering, now it is your turn to accept the solution.

fady_hasnaa 7-Apr-14 15:29pm

thanks my dear