如何在编程中让GET请求提前执行并在特定条件下处理请求结果？

let requestURL = 'http://aaa.com';
let extractedLink = null; // 用于存储提取到的链接
let requestFinished = false; // 请求完成标志

function fetchAndExtractLink() {
    GM_xmlhttpRequest({
        method: 'GET',
        url: requestURL,
        onload: function(response) {
            if (response.status === 200) {
                const parser = new DOMParser();
                const doc = parser.parseFromString(response.responseText, 'text/html');
                const linkElement = doc.querySelector('.item > a');
                extractedLink = linkElement ? linkElement.href : null;
            } else {
                console.error('GET request failed with status:', response.status);
            }
            requestFinished = true; // 设置请求完成标志
        },
        onerror: function(error) {
            console.error('GET request error:', error);
            requestFinished = true; // 即使出错也要设置完成标志
        }
    });
}

fetchAndExtractLink();

// 假设'myElement'是需要监听鼠标悬停的元素
document.getElementById('myElement').addEventListener('mouseover', function() {
    if (requestFinished) {
        if (extractedLink) {
            window.open(extractedLink);
        } else {
            console.log('No link found in the response.');
        }
    } else {
        console.log('Request is still in progress.');
    }
});