<div class="choose">

     choose a mode<br>

     <hr>

         <button type="submit" id="easy" onclick="easymode()"> Easy </button>

         <button type="submit" id="hard" onclick="hardmode()"> Hard </button>

         <button type="submit" id="crazy" onclick="crazymode()"> Crazy </button>

         <br><hr>

     </div>

     <script>

         /*easy*/

        function easymode()

        { var script=document.createElement("script");

script.setAttribute("type","text/javascript");

script.setAttribute("language","javascript");

script.setAttribute("src","baselevel.js");

document.getElementsByTagName("body")[0].appendChild(script);}

        /*hard*/

         function hardmode()

        { var script=document.createElement("script");

script.setAttribute("type","text/javascript");

script.setAttribute("language","javascript");

script.setAttribute("src","hardlevel.js");

document.getElementsByTagName("body")[0].appendChild(script);}

         /*crazy*/

         function crazymode()

        { var script=document.createElement("script");

script.setAttribute("type","text/javascript");

script.setAttribute("language","javascript");

script.setAttribute("src","crazylevel.js");

document.getElementsByTagName("body")[0].appendChild(script);}

</script>