保存一个外部域的图片

storefile

  var img = new Image,
      canvas = document.createElement("canvas"),
      ctx = canvas.getContext("2d"),
      src = "http://example.com/image"; // 外部域中的图片url
  img.crossOrigin = "Anonymous";
  
  img.onload = function() {
      canvas.width = img.width;
      canvas.height = img.height;
      ctx.drawImage( img, 0, 0 );
      localStorage.setItem( "savedImageData", canvas.toDataURL("image/png") );
  }
  img.src = src;
  // 在src图片已被缓存的情况下,确保load事件发生.
  if ( img.complete || img.complete === undefined ) {
      img.src = "data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///ywAAAAAAQABAAACAUwAOw==";
      img.src = src;
  }