判断接口是否支持跨域

打开浏览器，右键，选择检查，选择console

输入测试代码，然后回车，正常返回即可跨域请求

get请求

var xhr = new XMLHttpRequest();
xhr.open('GET', 'url');
xhr.send(null);
xhr.onload = function(e) {
    var xhr = e.target;
    console.log(xhr.responseText);
}

post请求：

var httpRequest = new XMLHttpRequest();
httpRequest.open('POST', 'url', true);
httpRequest.setRequestHeader("Content-type","application/json");
// 请求体
var obj = {
            "input": "I lvve buy some cakes"
        };
httpRequest.send(JSON.stringify(obj));
httpRequest.onreadystatechange = function () {
    if (httpRequest.readyState == 4 && httpRequest.status == 200) {
        var json = httpRequest.responseText;
        console.log(json);
    }
};

如果如下类似显示，则不可跨域请求