Why does file writing fail inside setInterval despite having correct permissions in Node.js?

The error message indicates that when the callback runs, Node is trying to open "database.json" in a location where it isn’t writable (or even isn’t found at all). One common culprit in such cases is the use of a relative path (“./database.json”). In asynchronous functions, especially when there’s other code running, it’s possible that the process’s current working directory (process.cwd()) has changed from what you expect.

Here are some troubleshooting steps and solutions:

1. Verify the Working Directory
   Add a log for the current working directory to confirm that it hasn’t changed unexpectedly:

   JAVASCRIPTCopied
   setInterval(() => {
     console.log("Current working directory:", process.cwd());
     console.log("USER:", process.env.USER); // root, as expected
     
     fs.access("./database.json", fs.constants.W_OK, (err) => {
       if (err) {
         console.error("Directory is not writable or file is not accessible");
       } else {
         console.log("Writable access verified");
       }
     });
   }, 2000);

2. Use an Absolute Path
   If you suspect that the working directory might be getting changed somewhere else in the code, consider using an absolute path for file operations. For example:

   JAVASCRIPTCopied
   const path = require('path');
   const absolutePath = path.resolve(__dirname, 'database.json');
   
   setInterval(() => {
     console.log("Accessing file at:", absolutePath);
     
     fs.access(absolutePath, fs.constants.W_OK, (err) => {
       if (err) {
         console.error("File not writable:", err);
       } else {
         console.log("Writable access verified");
       }
     });
   }, 2000);

3. Check for process.chdir Calls
   Review your code (or any libraries you might be using) to see if there is any call to process.chdir() that might accidentally be changing the working directory.

4. Concurrent File Access
   Although less likely, ensure that no other part of your program is holding a lock on the file or otherwise interfering with file access during your timer callback.

By confirming the current working directory and using an absolute path, you should be able to narrow down whether the issue is due to an unexpected cwd change or another factor affecting file access within your timer loop.