Question

I have following javascript to prevent user from entering invalid characters into a text field. It’s working well in chrome but not in firefox. It’s preventing the backspace key to be entered in the text field in firefox.

function onlyNumbers(evt) {
    var theEvent = evt || window.event;
    var key = theEvent.keyCode || theEvent.which;
    key = String.fromCharCode( key );
    var regex = /[0-9]|\./;
    if( !regex.test(key) ) {
        theEvent.returnValue = false;
        if(theEvent.preventDefault) theEvent.preventDefault(); 
    }
}

Can anyone please have a look and propose a fix for firefox to not prevent backspace key to act on a text field ?

Probably I guess, adding the regex for the backspace character would do the job here. Does anyone know, how to add the regex for matching the backspace

Edit:

Also, the above code has supposed to interrupted with the Tab key behaviour, I am not able to jump to next fields in the form using Tab key.

Answer 1

see http://jsfiddle.net/8ZJZD/1/

var el=document.getElementById('cnfMobileNo');
el.onkeydown=function onlyNumbers(evt) {
    var theEvent = evt || window.event;
    var key = theEvent.keyCode || theEvent.which;
    if(key===8){return;}
    key = String.fromCharCode(key);
    var regex = /[0-9]|\./;
    if( !regex.test(key) ) {
        theEvent.returnValue = false;
        if(theEvent.preventDefault) theEvent.preventDefault();
    }
}

Just use if(key===8){return;}

Edit:

If you want to exclude more keys, use

var el=document.getElementById('cnfMobileNo');
el.onkeydown=function onlyNumbers(evt) {
    var theEvent = evt || window.event,
        key = theEvent.keyCode || theEvent.which,
        exclusions=[8,9]; /*Add exceptions here */
    if(exclusions.indexOf(key)>-1){return;}
    key = String.fromCharCode(key);
    var regex = /[0-9]|\./;
    if( !regex.test(key) ) {
        theEvent.returnValue = false;
        if(theEvent.preventDefault) theEvent.preventDefault();
    }
}

See it here: http://jsfiddle.net/8ZJZD/2/

You can know the keyCode of each key using alert(key)

(before key = String.fromCharCode(key)).

You could also exclude

• The arrow keys: 37,38,39,40
• Enter: 13
• Context menu: 93
• Start and End: 36,35