js ajax 执行顺序

var xhr = new XMLHttpRequest();

xhr.open('GET', 'example.php', true); // true 表示异步

xhr.onreadystatechange = function() {
    if (xhr.readyState === 4 && xhr.status === 200) {
        // 请求成功，处理响应数据
        console.log(xhr.responseText);
    }
};

xhr.send();

console.log('开始发送请求');

var xhr = new XMLHttpRequest();
xhr.open('GET', 'example.php', true);
xhr.onreadystatechange = function() {
    if (xhr.readyState === 4 && xhr.status === 200) {
        console.log('请求成功，响应数据：', xhr.responseText);
    }
};
xhr.send();

console.log('请求已发送，继续执行后续代码');

function fetchData() {
    return new Promise((resolve, reject) => {
        var xhr = new XMLHttpRequest();
        xhr.open('GET', 'example.php', true);
        xhr.onreadystatechange = function() {
            if (xhr.readyState === 4) {
                if (xhr.status === 200) {