<canvas id="myCanvas" width="400" height="400"></canvas>

canvas {
  border: 1px solid #ccc;
}

window.addEventListener('load', eventWindowLoaded, false);

function eventWindowLoaded () {
  canvasApp(); //包含整个Canvas应用程序
}
function canvasSupport (e) {
  
	  return !!e.getContext;

}
function canvasApp () {
  var myCanvas = document.getElementById('myCanvas');

  if (!canvasSupport(myCanvas)) {
	  return; 
	}
  
  var ctx = myCanvas.getContext('2d');
  
  ctx.fillStyle = '#f36';
  ctx.fillRect(0,0,200,200);
  
}