Pipe websocket message to file

I have a websocket handler that writes a message to a file with the function below. However, with a large message, saving the file can take a long time. Is there a way to pipe the the websocket message directly to the file, or to speed up how long it takes to receive and save it?

var fs = require('fs');

function wsHandler(ws) {
    ws.on('message', function wsData(msg) { 
     
      try {
        let data = (JSON.parse(msg));
        /*data would be this:

             data = {'command':'saveFile', 
                     'fileName': 'test.txt', 
                     'fileData':'This is a test of the file data, 
                                 but imagine it is 4KB of information.'
                     }
        */
        try {
          switch(data.command) {

            case 'saveFile':
              fs.writeFileSync(data.fileName, data.fileData);
              break;
            
            
           }
        }
        catch(err){} 
       
      }
      catch(err){}
    });