AJAX:async javaScript and xml,异步 js 和 json
const ajax = (method, url, data, success, fail) => {
var request = new XMLHttpRequest()
request.open(method, url);
request.onreadystatechange = function () {
if (request.readyState === 4) { // 表示下载完成
if (request.status >= 200 && request.status < 300 || request.status === 304) {
// 表示成功的状态码,304表示内容不变,所以也算成功
success(request)
} else {
fail(request)
}
}
};
request.send();
}