Question

I have a function below where it doesn’t allow the user to type in letters in a textbox but it keeps saying event is undefined. Where and how am I suppose to define event?

Below is the function:

function isNumberKey(evt)
  {
     var charCode = (evt.which) ? evt.which : event.keyCode
     if (charCode > 31 && (charCode < 48 || charCode > 57))
        return false;

     return true;
  }

Below is the html where this could be used:

onkeypress="return isNumberKey(event)"

Answer 1

change

var charCode = (evt.which) ? evt.which : event.keyCode

to

var charCode = (evt.which) ? evt.which : evt.keyCode

or if you are using jQuery (you tagged it but aren’t using it) you could do

$('#textareaid').keypress(function(e) {
     if (e.which > 31 && (e.which < 48 || e.which > 57)) {
        e.preventDefault();
     }
});

where your html is

<textarea id="textareaid"></textarea>

See event.preventDefault()

Note on how to get key pressed using jQuery

To determine which character was entered, examine the event object
that is passed to the handler function. While browsers use differing
properties to store this information, jQuery normalizes the .which
property so you can reliably use it to retrieve the character code.

Taken from the .keypress() docs