XMLHttpRequest使用

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发送json类型数据

var request = new XMLHttpRequest();
request.open('post', '/address/dosomething');
var params = {
    name: '张三',
    age: 18
};
// 发json类型
request.setRequestHeader("Content-Type","application/json;charset=UTF-8");  //用POST的时候一定要有,缺少这句，后台无法获取参数
request.send(JSON.stringify(params));

request.onreadystatechange = function (){
    if(request.readyState === 4 && request.status === 200){
        // dealData(request.responseText)
    }
}

发送表单类型数据

var request = new XMLHttpRequest();
request.open('post', '/address/dosomething');
var params = 'name=zhangsan&age=18';
 // 发送表单类型
request.setRequestHeader("Content-Type","application/x-www-form-urlencoded;charset=UTF-8");  //用POST的时候一定要有,缺少这句，后台无法获取参数  
request.send(params);

request.onreadystatechange = function (){
    if(request.readyState === 4 && request.status === 200){
        // dealData(request.responseText)
    }
}

关于跨域：

跨域的控制在服务端，和浏览器端无关

//设置跨域 ，设置请求能携带cookie
res.header("Access-Control-Allow-Origin", req.headers['origin']); // 设置允许跨域,http发起段的域名都允许
// res.header("Access-Control-Allow-Origin", "*"); // 该资源可以被任意外域访问
// res.header("Access-Control-Allow-Origin", "http://foo.example"); // 仅允许http://foo.example域名下的请求跨域
res.header("Access-Control-Allow-Credentials", “true"); // 设置请求能携带cookie

参考文档：

1、http://www.ruanyifeng.com/blog/2012/09/xmlhttprequest_level_2.html

2、https://developer.mozilla.org/zh-CN/docs/Web/HTTP/Access_control_CORS