Returning updated config.json file (MERN app)

Question

I am using node file system module for the first time to store a config.json file that could be edited from front-end. I am able to read create config.json file and read the file separately.

However, I want to update the file and return the saved file in the same request. How do I do the same efficiently

//To Set config file & return data
router.post('/write-config', adminAuth, (req, res) => {
   console.log(`admin wants to update config`) ;

   const {config} = req.body ;

   try {
       fs.writeFile(__dirname+'/data/config.json', JSON.stringify(config), (err) => {
         if (err) throw err ;
         console.log('Configuration saved successfully.') ;
       });
       //res.json("ok") ;
       /* return the data from file which we just saved */ 
   }
   catch(err) {
       console.log(err.message) ;
       res.status(400).json(err.message) ;
   }
}) ;