How to request data across domains with jquery front-end

In front-end development, it is often necessary to request data from different servers. However, due to the restrictions of the same-origin policy, data cannot be directly requested across domains. To solve this problem, we can use the method provided by jQuery.

1. What is cross-domain request data

Cross-domain request data refers to obtaining data by sending a request to another server through the client (browser) in front-end development data. For security reasons, browsers restrict requests from servers with different origins. Same origin means that the protocol, port and host name of the two pages are the same. A common situation for requesting data across domains is to request data from another server through Ajax on the front-end page.

2. Why cross-domain data request is needed

Cross-domain data request is a very common situation in front-end development. There are several reasons:

• Separate front-end and back-end logic: Front-end and back-end development are often completed by two different teams, and they require different servers to run their respective codes. By requesting data across domains, the logical separation between the front end and the back end can be made clearer.
• Save resources: Some commercial services may only provide API interfaces and not front-end resources. At this time, if you need to call the service, you need to request data across domains.
• Multiple front-end servers share data: Sometimes, different front-end servers need to access the same back-end service, and in this case, cross-domain data requests are required.

3. Methods to solve cross-domain data request

Due to the restrictions of the same-origin policy, cross-domain data cannot be requested directly, but we can use the following solutions:

• JSONP: Although JavaScript does not natively support cross-domain requests, you can use the src attribute of the <script> tag to request data from other servers. This method is JSONP. However, this method requires the server to support returning data in JSONP format, and is vulnerable to XSS attacks. </script>
• CORS: Cross-Origin Resource Sharing (CORS) is a browser technology that allows the server to tell the browser which domains are allowed to access through HTTP headers. But this method requires server-side support.
• Proxy: The front-end server sends requests to other servers through a back-end server, and then returns the results to the front-end. However, this method requires front-end developers to understand the back-end server technology, and the server overhead is large.

4. Using jQuery to request data across domains

jQuery provides some methods to help us request data across domains:

• $.ajax() method: The most commonly used Ajax method in jQuery. It can specify the data format that the server needs to receive by setting the contentType attribute, and the dataType attribute to specify the data format returned by the server.
• $.getJSON() method: This method is a simple encapsulation of the $.ajax() method, used to obtain data in JSON format through a GET request.
• $.getScript() method: This method is a simple encapsulation of the $.ajax() method, used to obtain JavaScript files through GET requests.
• $.postMessage() method: This method was introduced in HTML5 for secure cross-domain communication between multiple windows/pages.

The specific code is as follows:

$.ajax({
   url: 'http://example.com/test.php',
   dataType: 'jsonp',
   success: function(data){
      console.log(data);
   },
   error: function(){
      console.log("error");
   }
});

$.getJSON('http://example.com/test.php', function(data){
  console.log(data);
});

$.getScript('http://example.com/test.js', function(){
  console.log("script loaded");
});

window.postMessage("message", "http://example.com");

In short, in the process of using jQuery to request data across domains, you need to set the request headers, parameters and callback functions appropriately to ensure smooth operation. Get target data.

5. Conclusion

Cross-domain data request is a very common situation in front-end development. Although the restrictions of the same-origin policy make it difficult to request data across domains, the problem can be solved using methods such as JSONP, CORS, and proxies. Through the methods provided by jQuery, the process of requesting data across domains can be made simpler and more efficient.

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