SOURCE

console.log("2222")
function setupGLEnv(canvasID) {
    canvas = document.getElementById(canvasID);
    gl = canvas.getContext('webgl') || canvas.getContext('experimental-webgl');
    if (!gl) {
      alert('天呐！您的浏览器竟然不支持WebGL，快去更新浏览器吧。');
    }
}
function renderLoop() {
  now = (new Date()).getTime();
  deltaTime = now - lastRenderTime;
  lastRenderTime = now;
  elapsedTime += deltaTime;
  
  render(deltaTime, elapsedTime);
  
  collectedFrameDuration += deltaTime;
  collectedFrameCount++;
  if (collectedFrameCount >= 10) {
    fps = parseInt(1000.0 * collectedFrameCount / collectedFrameDuration);
    if (isNaN(fps) == false || fps < 1000) {
      glInfoNode.textContent = "FPS: " + fps;
    }
    collectedFrameCount = 0;
    collectedFrameDuration = 0;
  }
  requestAnimationFrame(renderLoop);
}
function render(deltaTime, elapesdTime) {
    gl.clearColor(1.0, .0, .0, 0.0);
    gl.clear(gl.COLOR_BUFFER_BIT);
}
window.onload = function() {
  setupGLEnv('glCanvas');
  glInfoNode = document.getElementById("glInfo");
  resize(canvas.parentElement.clientWidth, canvas.parentElement.clientHeight - 1);
  renderLoop();
}

<div style="width: 100%; height: 300px; position:relative; background:rgba(0,0,0,0);">
  <canvas id="glCanvas" width="400" height="300">
    Your browser doesn't appear to support the 
    <code><canvas></code> element.
  </canvas>
  <div id="glInfo" style=""></div>
</div>