解决跨域问题， 网上成熟的解决方案，我是直接拷贝的

app.all("*",function(req,res,next){

    res.header("ACCESS-Control-Allow-Origin","*");

    res.header("ACCESS-Control-Allow-Headers","X-Requested-Width");

    res.header("ACCESS-Control-Allow-Methods","PUT,POST,GET,DELETE,OPTIONS");

    res.header("X-Powered-By",'3.2.1');

    res.header("Content-Type","application/json;charset=utf-8");

    next();

});