Disable backspace and delete key with javascript in IE

Anyone know how can I disable backspace and delete key with Javascript in IE? This is my code below, but seems it's not work for IE but fine for Mozilla.

onkeydown="return isNumberKey(event,this)"

function isNumberKey(evt, obj)
{

    var charCode = (evt.which) ? evt.which : evt.keyCode
    if (charCode == 8 || charCode == 46) return false;

    return true;
}

How do I turn off backspace delete?

Press the "Ins" key to toggle overtype mode off. Depending on your keyboard model, this key may also be labeled "Insert." If you simply want to disable overtype mode but keep the ability to toggle it back on, you are done.

This code cancels backspace action.

window.onkeydown = function (event) {

    if (event.which == 8) { 

         event.preventDefault();   // turn off browser transition to the previous page 

                 // put here code you need 

        }; 

};