JS Customizeable Graph

<html>
<body onload="draw();">
<canvas id="canvas" width="2000" height="2000" style="1px background:black"></canvas>
</body>
</html>
<script>
function draw() {
var ee=prompt('Enter Level:');
ctx=document.getElementById('canvas').getContext('2d');
var img = new Image();
img.onload = function(){
ctx.scale(2,2);
ctx.drawImage(img,0,0);
ctx.beginPath();
ctx.strokeStyle='darkred';
ctx.moveTo(ee,115);
ctx.lineTo(115,15);
ctx.stroke();
};
img.src='https://mdn.mozillademos.org/files/5395/backdrop.png';
}
</script>