<!DOCTYPE html>
<html>
    <head>
        <meta charset="utf-8">
        <title></title>
        <script>
            window.onload = function() {
                var input = document.getElementsByTagName("input")[0];
                input.value = "";
                input.onkeydown = function() {
                    alert(1);
                };
                input.onkeypress = function() {
                    alert(2);
                };
                input.onkeyup = function() {
                    alert(3);
                };

            };
        </script>
    </head>
    <body>
        <p><input></p>
    </body>
</html>