How to get GET requests to be executed in advance and process the request results under specific conditions in programming?

Asynchronous GET request and conditional result processing

This article discusses how to execute GET requests in advance in programming and process their results after specific conditions are met. This is useful in scenarios where you need to respond to user interactions (such as mouse hover events) and rely on the results of a network request. Simply using delay waiting for requests to be completed is not the best solution because it will affect the user experience.

The following scheme utilizes the asynchronous request feature to avoid unnecessary delay waiting.

First, we use GM_xmlhttpRequest (Greasemonkey/Tampermonkey) to perform the GET request. For clarity, we replaced getwebsite in the original code with a more descriptive function name.

 let requestURL = 'http://aaa.com';
let extractedLink = null; // Used to store the extracted link let requestFinished = false; // Request completion flag 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; // Set the request completion flag},
        oneError: function(error) {
            console.error('GET request error:', error);
            requestFinished = true; // Set the completion flag even if there is an error}
    });
}

fetchAndExtractLink();

This code performs a GET request and extracts the first link that .item > a selector matches from the response. The key lies in the requestFinished flag, which indicates whether the request has been completed (success or failure).

Next, in the mouseover event handler function, we check the requestFinished flag:

 // Suppose 'myElement' is the element that needs to listen for mouse hover 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.');
    }
});

This event listener is triggered when the mouse is hovered over myElement . It checks requestFinished , and the link will only be opened after the request is completed and the link is extracted. If no link is extracted, the corresponding information will be output. This avoids unnecessary delays and provides more reliable error handling.

This method elegantly solves the problem of handling GET request results under specific conditions through asynchronous operations and status flags, improving user experience and code robustness. Remember to replace 'myElement' with the ID of the actual element.

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