I'm trying to remove a character as it's typed/keyed up to test whether it's a number or not, if it is a number, keep it, if not, remove it. It can be more than one digit. for example, I type in a "d", it should be deleted from the textbox. I then type a "1", where it should stay in the textbox. I then type a 4 and it also stays so the textbox now reads "14". Then I type "g", which should be deleted. Then I type a "5" and now the text box reads 145. This is what I have so far.

```
   $("#txtTestNumbersOnlyRegex").keyup(function () {

            $("#txtTestNumbersOnlyRegex").val(function (index, value) {
                var keyPressed = value.substr(0, value.length - 1);
                var regEx = new RegExp("/^5$/");
                if(!regEx.test(keyPressed)) {
                    alert("true");
                    return value.substr(0, value.length - 1);
                }                   
            });      

        });            

```