jquery's fetch synchronous request

As web applications continue to evolve, client-side JavaScript is becoming more and more important, and in JavaScript, jQuery is one of the most popular libraries.

jQuery is a fast, small, feature-rich, cross-browser JavaScript library that makes traversing and manipulating HTML documents easier and more convenient. In jQuery, we usually use AJAX technology for asynchronous data requests. However, in some cases, we need to use synchronous requests. The solution to this problem is to use jQuery's fetch synchronous request.

This article will introduce the use of jQuery's fetch synchronous request, including its basic syntax and solutions to common problems.

Basic syntax of fetch synchronous request

When using jQuery's fetch synchronous request, you need to pass a parameter containing async:false in the AJAX request. This parameter can ensure that the asynchronous request will not continue to execute the code before returning the response, and wait for the server to respond before continuing to execute the JavaScript code.

For example, we initiate a synchronous GET request through jQuery:

$.ajax({
    url:"http://localhost:8080/api/data",
    dataType:"json",
    async:false,
    success: function(data) {
        console.log(data);
    }
});

Let’s take a look at the basic syntax of the fetch synchronous request:

$.ajax({
    url: 'example.json',
    async: false,
    dataType: 'json',
    success: (data) => console.log(data)
});

In the above code, we use jQuery's $.ajax() function passes in an object containing the async:false parameter. At the same time, we specify the URL and data type of the request, and print out the response data after the request is successful.

Common problems and solutions for fetch synchronous requests

1. Fetch synchronous requests may cause program blocking

When using fetch synchronous requests, if the server response time is too long, Will block JavaScript execution. This means that any JavaScript code on the page will not be able to execute until the response is returned. Additionally, the request may remain pending until it times out or the server responds.

Solution: If you want to avoid program blocking, it is recommended to use asynchronous requests, or break the requests into smaller parts.

2. The fetch synchronous request cannot send cookies synchronously

The fetch request will not send cookies to the server by default, which is different from the asynchronous request. If you want to use cookies, you need to set the value of parameter credentials to 'include'.

$.ajax({
    url: 'example.json',
    async: false,
    dataType: 'json',
    credentials: 'include',
    success: (data) => console.log(data)
});

3. The fetch synchronous request may encounter cross-domain problems

Due to the same-origin policy restriction of the browser, the fetch synchronous request may be intercepted by cross-domain. At this point, the browser may block the request from being sent.

Solution: You can use JSONP (JSON with Padding) technology or a proxy server to avoid cross-domain problems.

4. The fetch synchronous request does not support all HTTP methods

The fetch synchronous request only supports the GET and POST methods. If you need to use other HTTP methods, you need to use asynchronous requests.

5. The fetch synchronous request will block page life cycle events

If a synchronous request occurs during page life cycle events (such as onbeforeunload), the page will be Blocks until response returns. This may cause the page to hang for a long time, giving users a bad experience.

Solution: Avoid using fetch synchronous requests in page life cycle events.

Summary

This article introduces how to use jQuery’s fetch synchronous request and how to solve common problems. While using synchronous requests is convenient in some situations, there are some potential issues to be aware of. To improve the user experience of web applications, it is recommended to use asynchronous requests whenever possible.

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