keyCode issue - Can't prevent entering the % character

Question

In my HTML page there is an input text field. I want only number key and left/right arrow on the keyboard can be entered. I tried the following JavaScript but met an issue.

<input onkeypress="return allowNumberOnly(event)" />

function allowNumberOnly(event) {
    event = event || window.event;
    var charCode = (event.which) ? event.which : event.keyCode;

    //keyCode 48-57 represent the number 0-9
    //keyCode 37,39 represent the Left and Right arrow
    //keyCode 46 represent the Delete key
    //keyCode 8 represent the Backspace key

    return charCode == 37 || charCode == 39 || charCode == 46 || charCode == 8
              || (charCode >= 48 && charCode <= 57);
}

After testing this code, I found a problem that the keyCode of left arrow and % special character are both 37. So I can't prevent user entering % character meanwhile allowing the Left arrow. I have no idea why this would happen. I always thought the keyCode should be unique for each key on the keyboard. I thought of using onkeyup instead of onkeypress. But the onkeyup would allow user entering the invalid character first, then remove from the input text. This behavior is not what I want. Any suggestion would be appreciated.

I debugged the code in FireFox and found the following difference.

1. If enter %, event.which == 37 and event.keyCode == 0
2. If enter Left Arrow, event.which == 0 and event.keyCode == 37

The problem seems to be resolved by using this difference. I will continue to try in IE and Chrome.

Answer 1

This link has more info about Keyboard events

http://unixpapa.com/js/key.html

Also I made jQuery version

$('input').keypress( function( e ){ 

    var code = e.which || e.keyCode ; 

    if ( !( e.shiftKey == false &&
            (
               code == 46 ||
               code == 8 ||
               code == 37 ||
               code == 39 ||
               ( code >= 48 && code <= 57 ) 
            )
         )
    ){

         e.preventDefault();                   
    }

});

check it on http://jsfiddle.net/UGpUJ/

Answer 2

Check Bryant Williams' answer to this question:

how can i track arrow keys in Chrome and IE?

He suggests checking if the charCode==0, or checking for the shift key being pressed.

Answer 3

I came up with this a while ago:

var numbersOnly = function(e){
    var charCode = (typeof e.which === "number") ? e.which : e.keyCode,
        chr = String.fromCharCode(charCode); //convert it to a character

    if(isNaN(parseInt(chr, 10))) e.preventDefault();
}

Usage:

<input type="text" name="phoneNumber" onkeypress="numbersOnly(event);">

Basically what we're doing here is getting the key code used, converting that to its char code equivalent, and then testing the char code instead of the key code. I find this method to work much better than any other I've come across and it works pretty nicely.

JS Bin Example.