node返回数据时，设置下面头部跨域实现跨域

res.setHeader('Access-Control-Allow-Origin','*');
res.setHeader('Access-Control-Allow-Headers', 
'Content-Type, Content-Length, Authorization, 
Accept, X-Requested-With , yourHeaderFeild');
res.setHeader('Access-Control-Allow-Methods', 'PUT, POST, GET, DELETE, OPTIONS');