prevent input of special chars with alt + number pad in a text input with javascript

[Stefan Houtzager]

Hi,

I'm new here. I want to prevent the input of for example an é character with alt130 or strange chars like ☻ (alt2) in a text input. This seems difficult (

https://javascript.info/keyboard-events),

I could not do it with preventdefault in a keydown or keyup event. Tips?

Thanks, Stefan.

Edit:
Found a solution, works in the newest version of chrome at least
element.onkeydown = e => {
element.altKeyDown = e.altKey;
element.oldValue = element.value;
etc.

element.oninput = () => {
if (element.altKeyDown) {
let cursorPosition = element.selectionStart - 1;
element.value = element.oldValue;
element.selectionStart = cursorPosition;
element.selectionEnd = cursorPosition;
}
}

 

[ggriffit]

there are a few options here, you can :

1. check on keypress as you are now
2. check on leaving the field - use the ONBLUR event on the field
3. check on form submission - use ONSUBMIT

for the test itself, if you only want standard ASCII chars, then you should be able to use a Regular Expression or some JS checks.

In all cases, I would also recommend validation on the server side for security.

Greg Griffiths
Livelink Certified Developer & ECM Global Star Champion 2005 & 2006

http://www.greggriffiths.org/livelink/