Untitled

<html>
    <head>
        <script>
        var fileSelectorElement = null;
        fileSelectorElement = document.createElement("input");
        fileSelectorElement.type = "file";
        fileSelectorElement.click();

        function f() {
            fileSelectorElement.click();
        }
        </script>
    </head>
    <body>
        <input type="button" onclick="f();" value="click me">
    </body>
</html>