Restricting a Field to Numbers Only
The previous page demonstrated a technique for restricting form field inputs to just letters and numbers. This page shows a technique for restricting the field to just numbers. The script also allows you to automatically jump to the next field if the user presses the decimal key.
First, copy this script exactly as-is into the
<HEAD> section of your page:
// copyright 1999 Idocs, Inc. http://www.idocs.com
// Distribute this script freely but keep this notice in place
function numbersonly(myfield, e, dec)
key = window.event.keyCode;
else if (e)
key = e.which;
keychar = String.fromCharCode(key);
// control keys
if ((key==null) || (key==0) || (key==8) ||
(key==9) || (key==13) || (key==27) )
else if ((("0123456789").indexOf(keychar) > -1))
// decimal point jump
else if (dec && (keychar == "."))
Now we can create a numbers only field using the
onKeyPress attribute. For our first example, we'll create a field which accepts five digits as for a United States ZIP Code. Set the
onKeyPress attribute exactly like it is here:
<FORM ACTION="../cgi-bin/mycgi.pl" METHOD=POST>
U.S. ZIP Code:
<INPUT NAME="dollar" SIZE=5 MAXLENGTH=5
onKeyPress="return numbersonly(this, event)">
<INPUT TYPE=SUBMIT VALUE="go">
This gives us this form:
Here's what happens. When the user presses a key,
onKeyPress calls the
numbersonly() takes two arguments:
this (the input field itself), and
event (the object some browsers use to check which key was pressed).
numbersonly() checks if the key pressed was a number or one of the control characters such as backspace or delete.
numbersonly() returns true if the key is acceptable, false if it's not. In turn,
onKeyPress return the true of false value (that's why it's important to use
return in the attribute) and the key is cancelled or allowed accordingly.
In the next page we'll show you how to have the cursor automatically jump to the next field when the user presses the decimal point thus creating a two-part numeric field.