You are looking at a base game engine

<html>
<head>
<script>
// setup global variables for use through the code..
var distance_x = 3;
var distance_y = 3;
var screen_top = 10;
var screen_left = 10;
var screen_height = 300;
var screen_width = 500;

if(window.Event){ // cature keypresses..
  document.captureEvents(Event.KEYDOWN); document.onkeydown = setkey;
}else{
  document.onkeydown = function(){
   return setkey(event);
  }
}

function setkey(event){ // what to do each time a key is pressed..
    var obj = document.getElementById('ananything');
    obj.x = parseInt(obj.style.left); // get the objects X position
    obj.y = parseInt(obj.style.top);  // get the objects Y position
    obj.w = parseInt(obj.offsetWidth); // get the objects width
    obj.h = parseInt(obj.offsetHeight);  // get the objects height
    // alert(event.which); // use this to find out what key is pressed

 if((event.which==13)||(event.keyCode==13)){
  alert("You have pressed the enter key");
 }

 if((event.which==37)||(event.keyCode==37)){ obj.x = obj.x - distance_x; } // left
 if((event.which==39)||(event.keyCode==39)){ obj.x = obj.x + distance_x; } // right
 if((event.which==38)||(event.keyCode==38)){ obj.y = obj.y - distance_y; } // up
 if((event.which==40)||(event.keyCode==40)){ obj.y = obj.y + distance_y; } // down

 if((obj.y >= screen_top)&&(obj.y<= screen_top+screen_height-obj.h)){ obj.style.top = obj.y;} // update Y position..
 if((obj.x >= screen_left)&&(obj.x<= screen_left+screen_width-obj.w)){ obj.style.left = obj.x;} // update X position..

 document.title = obj.x + "x" + obj.y + " / " + obj.w + "x" + obj.h; // show this in the title bar
}

function setup(){ // set starting opsition of objects
 document.getElementById('ananything').style.left=300;
 document.getElementById('ananything').style.top=100;
}
</script>

<style>
#ananything{position:absolute;background:skyblue;color:lightgreen;}
#area{position:absolute;left:10px;top:10px;width:500px;height:300px;background:green;}
</style>
</head>
 <body onLoad="setup()">
  This is the webpage, I encourage you to type something
 <div id="area">
 </div>
  <div id="ananything">
   hello
  </div>
 </body>
</html>