原谅我这个伸手党，完全是头大了。
上代码：

var qr_image = require('qr-image');  
var images = require('images');
var request = require('request');
var fs = require('fs');

var logo = request('http:/\/wx.qlogo.cn\/mmopen\/PiajxSqBRaEKqqa31ybC79PqVmErpI2QiapLA5yxT9ampXSa1WrDxcTc6AokhZpBBoOvDYFwTJ5aP6Gvtarcib70w\/64')
.pipe(fs.createWriteStream('logo.jpeg'));
var qr = qr_image.imageSync('http://weixin.qq.com/q/027920JGB8eZ010000M07Q');
var width = images(qr).width() /2 ;
var height = images(qr).height() /2;
var size = width/2;

//images(qr).draw(images('logo.jpeg').size(size),width-size/2,height-size/2).save('t11est.jpeg',{quality:50});

我想等logo写入完成后执行注释的代码。请问如何写？
谢谢大神?