In below section of code, I want to read selected number of bytes from serial port. But it's reading 1 byte every time.

var BYTES_TO_READ  = 1
const { SerialPort } = require('serialport')
const fs = require('fs');
const { ByteLengthParser } = require('@serialport/parser-byte-length')
const port = new SerialPort({ path: 'COM7', baudRate: 576000 }) 
const parser = port.pipe(new ByteLengthParser({ length: BYTES_TO_READ }))
parser.on('data', function(data)
{
    console.log(data);
    fs.appendFile(log_path, data.toString("utf8"), function (err) 
    {
       if (data.slice(0,1).toString('hex') === '54')
       {
          BYTES_TO_READ = 30
       }
    }
}```