Hey all,

I'm writing an event listener that is trapping for certain keys (single quote & ampersand mainly) in a text input field.

I'm able to determine the key press through the keyCode. If an ampersand or single quote comes up, I give an alert box that those entries are not valid.

However, after the alert, it still writes the single quote or ampersand into text field.

I tried to get the length of the field and do a substring of the length -1, hoping to kill the ampersand or single quote. But it doesn't work. It cuts off a legitimate character and then writes in the single quote or ampersand.

I'm suspecting there's some sort of key buffer, but I can't seem to locate information on the web.

Here is the function code. I only wrote it for the ampersand.

function checkText(evt,lcID)
{
var charCode = (evt.which) ? evt.which : event.keyCode
switch(charCode)
{
case 38:
{ alert("Ampersands are not allowed");
var lcText = document.getElementById(lcID).value;
var lnLen = document.getElementById(lcID).value.length;
lnLen = lnLen-2;
document.getElementById(lcID).value = lcText.substr(0,lnLen);
break; }
case 39:
{ alert("Single quotes are not allowed");
var lcText = document.getElementById(lcID).value;
break; }
default: { break; }
}
}

Hope anyone can shed some light.

Thanks
Donna

Please use code tags.

In your HTML you could add something like this:

<input type="text" ... onKeyUp="return checkThis();" />

Then if the key is considered invalid, return false to disable the keystroke.

Be advised that this won't ensure one has not entered those keys -- 2 clicks to disabled javascript and I bypass your security. Be sure to sanitize data on the server too.

Jeremy's approach is the best one, but I just wanted to add that the reason your code isn't working is that you're trapping the wrong event. KeyDown and KeyPress both fire before characters are added to the textbox, so the offending quote won't be there when your handler triggers. If you hooked into KeyUp instead it would work.

Edit: That is to say, it will almost work. KeyUp only fires once per key stroke, no matter how long you hold the key down...