Keydown function to prevent letters - How to load function before key is entered

Question

I've taken a code snippet from a different closed post, which mainly works well, apart from one aspect.

1. I have an input field which I need to be numeric only
2. I need to allow for the use of a full stop
3. The code below works fantastically in allowing the above to happen
4. The issue is that the function isn't called until something has been entered into the input field
5. Unfortunately, this means a special character or letter can be entered, which then triggers the function to run

Is there a way to ensure that the function is run immediately so that all special characters and letters are prevented? (apart from a full stop and numbers)

It's also worth noting, that I'm working in IE8.

function numberValidation(){
  $("#txtboxToFilter").keydown(function (e) {
        // Allow: backspace, delete, tab, escape, enter and .
    if ($.inArray(e.keyCode, [46, 8, 9, 27, 13, 110, 190]) !== -1 ||
         // Allow: Ctrl+A
        (e.keyCode == 65 && e.ctrlKey === true) ||
         // Allow: Ctrl+C
        (e.keyCode == 67 && e.ctrlKey === true) ||
         // Allow: Ctrl+X
        (e.keyCode == 88 && e.ctrlKey === true) ||
         // Allow: home, end, left, right
        (e.keyCode >= 35 && e.keyCode <= 39)) {
             // let it happen, don't do anything
             return;
    }
    // Ensure that it is a number and stop the keypress
    if ((e.shiftKey || (e.keyCode < 48 || e.keyCode > 57)) && (e.keyCode < 96 || e.keyCode > 105)) {
        e.preventDefault();
    }
});

}

Answer 1

You are not calling the function! Either call it on $(document).ready() like this:

$(document).ready(function(){
   numberValidation();
});

Or, give this in the $(document).ready() instead:

$(document).ready(function () {
  $("#txtboxToFilter").keydown(function (e) {
    // Allow: backspace, delete, tab, escape, enter and .
  });
});

Snippet

$(document).ready(function () {
  $("#txtboxToFilter").keydown(function (e) {
    // Allow: backspace, delete, tab, escape, enter and .
    if ($.inArray(e.keyCode, [46, 8, 9, 27, 13, 110, 190]) !== -1 ||
        // Allow: Ctrl+A
        (e.keyCode == 65 && e.ctrlKey === true) ||
        // Allow: Ctrl+C
        (e.keyCode == 67 && e.ctrlKey === true) ||
        // Allow: Ctrl+X
        (e.keyCode == 88 && e.ctrlKey === true) ||
        // Allow: home, end, left, right
        (e.keyCode >= 35 && e.keyCode <= 39)) {
      // let it happen, don't do anything
      return;
    }
    // Ensure that it is a number and stop the keypress
    if ((e.shiftKey || (e.keyCode < 48 || e.keyCode > 57)) && (e.keyCode < 96 || e.keyCode > 105)) {
      e.preventDefault();
    }
  });
});

<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js"></script>
<input id="txtboxToFilter" type="text" />

Answer 2

call the function on load like this

$(function(){
   numberValidation();
});