Html node.js画布图像作为“背景”

是否可以使用node.js npm canvas“在图像中填充图案”

我试着按照这个方法做，但我错了

返回新的画布图像； ^ 错误：给定的映像尚未完成加载

   exports.convertImg = function(story){

        var Canvas = require('canvas')
        , canvas = new Canvas(200,200)
        , ctx = canvas.getContext('2d'),textDimensions, img = new Canvas.Image;

          var textWidth = ctx.measureText(story).width;

          img.src = "/images/fillimage.png";
          var buffer = new Buffer(story, "base64"),length=buffer.length;

          var pat=ctx.createPattern(img,"repeat");
          ctx.fillStyle = pat;

          ctx.font = "20px verdana";

          var x= (canvas.width -200) / 2;
          var y= 60;
          wrapText(ctx,story,x,y,200,200);

          var imges =  canvas.toDataURL();
          var data = imges.replace(/^data:image\/\w+;base64,/, "");
          var buf = new Buffer(data, 'base64');

          var length=buf.length;
          return  images;
        }

如何在画布填充图案中填充背景图像。请帮帮我

谢谢