[JavaScript] 2D-Canvas Setup

<!DOCTYPE html>
<html>
  <head>
    <meta charset="utf-8">
    <title>Canvas Test</title>
  </head>
  <body>
    <canvas></canvas>
    <script>
	let canvas = document.querySelector('canvas');
	let ctx = canvas.getContext('2d');

	let width = canvas.width = window.innerWidth;
	let height = canvas.height = window.innerHeight;
	
	...
	</script>
  </body>
</html>