Return to tutorial on Moving image across screen

Moving image vertically within two boundaries Moving image horizontally within two boundaries Moving image randomly within four boundaries Moving image by using up, down, left & right keys Moving two images corssing
Source Code is here

JavaScript part
<script >
<!--
function reset1(){
clearTimeout(my_time);
document.getElementById('i1').style.left= "500px";
document.getElementById('i1').style.top= "100px";
document.getElementById("msg").innerHTML="";
}

function disp(){
var step=1; // Change this step value
//alert("Hello");
var y=document.getElementById('i1').offsetTop;
var x=document.getElementById('i1').offsetLeft;
document.getElementById("msg").innerHTML="X: " + x  + " Y : " + y
if(y < 400 ){y= y +step;
document.getElementById('i1').style.top= y + "px"; // vertical movment
}else{
if(x < 800){x= x +step;
document.getElementById('i1').style.left= x + "px"; // horizontal movment
}
}
//////////////////////
}

function timer(){
disp();
my_time=setTimeout('timer()',10);
}
//-->
</script>
HTML
<img src=images/help.jpg id='i1' style="position:absolute; left: 500; top: 100;">
<br><br><br><br>
<input type=button onClick=timer() value='Start'>
<input type=button onClick=reset1() value='Reset'>
<div id='msg'></div>