JS POST request failed, but POSTMAN succeeded: How to troubleshoot browser Fetch API request issues?

Browser Fetch API POST request failed, but Postman succeeded?

When sending POST requests using JavaScript's Fetch API, I encountered a problem: the browser failed to execute, but Postman was able to successfully send the same request. This article will analyze the possible causes and solutions.

Problem: The developer uses the Fetch API to send a POST request, the body contains JSON data, and uses Basic authentication. Execution in the browser always fails, entering the catch block, while Postman can successfully get the response.

Possible causes and solutions:

1. Cross-domain issues: This is the most common reason. Browser security mechanisms restrict cross-domain requests. A cross-domain error occurs if the Fetch requests the target URL different from the front-end page domain name, port, or protocol. Postman is not subject to this restriction. Be sure to check whether the URL is exactly the same as the front-end page (domain name, port, protocol). If it is inconsistent, the server needs to configure CORS (cross-domain resource sharing) to allow cross-domain requests.

2. Detailed cross-domain inspection: Cross-domain includes cross-protocols (http request https), cross-port (such as 80 port request 8080 port), cross-domain name, etc. These three aspects need to be carefully checked to ensure that the front and back end URLs are exactly matched, or CORS is correctly configured on the server side.

3. Fetch request build error: Even if the code seems complete, there may still be subtle errors. For example, JSON.stringify(Body) may not correctly serialize the request body as a JSON string, or Content-Type setting in headers is incorrect. Carefully check the request body Body content and headers settings to ensure that it meets server expectations.

4. Other potential errors: Exception information captured by catch block ex may contain more detailed error information, which helps locate the problem. Check if the log output mechanism ( FR.Logger.error(ex);FR.Msg.toast(...) ) works properly and check the full code, as the provided code snippet may not be the entire cause of the problem.

By carefully checking the above points and combining the detailed error information of the browser console, the problem of Fetch POST request failure can be effectively solved.

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