Professional JavaScript For Web Developers

Chapter 11
To use this method, insert it into the HTML code for a text box (either or ) along
with the invalidchars attribute:
This one function can be used to block characters in a variety of useful ways:
Allowing valid characters
Naturally, the other method of restricting user input is to only allow certain characters in a text box.
Once again, the easiest way to accomplish this is to add an HTML attribute to a text box:
This example would allow the numbers 0 through 9 only, and no other characters. Naturally, you’ll need
to have an allowChars() method that does the opposite of the blockChars() method:
TextUtil.allowChars = function (oTextbox, oEvent) {
oEvent = EventUtil.formatEvent(oEvent);
var sValidChars = oTextbox.getAttribute(“validchars”);
var sChar = String.fromCharCode(oEvent.charCode);
var bIsValidChar = sValidChars.indexOf(sChar) > -1;
};
return bIsValidChar || oEvent.ctrlKey;
As you can see, the allowChars() has a lot in common with blockChars(): It accepts the text box and
the event object as arguments; it formats the event object using EventUtil.formatEvent(); it stores
the character that will be entered into the text box in a variable using String.fromCharCode(). The
350