Javascript numbers only

This script can be used for input fields which may contain only numbers.

Example
(html)
onKeyPress="return numbersonly(this, event)"

(javascript)
function numbersonly(myfield, e, dec){
var key;
var keychar;

if (window.event)
key = window.event.keyCode;
else if (e)
key = e.which;
else
return true;
keychar = String.fromCharCode(key);

// control keys
if ((key==null) (key==0) (key==8) (key==9) (key==13) (key==27) )
return true;

// numbers
else if ((("0123456789").indexOf(keychar) > -1))
return true;
// decimal point jump
else if (dec && (keychar == "."))
{ myfield.form.elements[dec].focus();
return false;
}
else
return false;
}