use js to call js

Go directly to the source code:

 <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>