fswatch_untrack.mjs

const fs = require('fs');
const process = require('process');
const child_process = require('child_process');

const filename = 'test.mjs'

const x = fs.watch(filename, (t, f) => {
  console.log(`eventType: ${t}, file: ${f}`)

  try {
    console.log(child_process.execSync(`ls -lah "${filename}"`,  { encoding: 'utf-8' }))
  } catch (e) {
    // ignore error
  }
});

console.log('start watching')

console.log('first write')
child_process.exec(`vim -c ":wq" "${filename}"`).on('close', () => {

  console.log('second write')
  child_process.exec(`vim -c ":wq" "${filename}"`).on('close', () => {

    console.log('end')
    console.log('もしも2回目の書込みでログが出なかったら、監視から外れている証拠。')
    x.close()
  })
})