发送Promise请求出现以下错误origin ‘null‘ has been blocked by CORS policy

错误如下

Access to XMLHttpRequest at 'http://localhost:9090/data' from origin 'null' has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present on the requested resource.

问题

出现了跨域访问问题

解决方法

用express设置允许跨域访问服务，代码如下：

// 引入express框架
var express=require("express");
// 创建web服务器
var app=express();
// 设置允许跨域访问该服务
app.all('*', function (req, res, next) {
	res.header('Access-Control-Allow-Origin', '*');
	res.header('Access-Control-Allow-Headers', 'Content-Type');
	res.header('Access-Control-Allow-Methods', '*');
	res.header('Access-Control-Allow-Headers', 'X-Requested-With');
	next();
});