app.post('/upload', function(req, res){
 //接收前台POST过来的base64
 var imgData = req.body.imgData;
 //过滤data:URL
 var base64Data = imgData.replace(/^data:image\/\w+;base64,/, "");
 var dataBuffer = new Buffer(base64Data, 'base64');
 fs.writeFile("image.png", dataBuffer, function(err) {
 if(err){
 res.send(err);
 }else{
 res.send("保存成功！");
 }
 });
});