lib/core/generator.js
function startWatcher (entryPoint, callback) {
  if (config.commands.build.dev) {
    // Delete the assets (CSS/etc.) before.
    // They might not be there, but we must ensure that they are properly
    // deleted.
    //
    // This is necessary, otherwise, remaining copied CSS files will have
    // an higher priority than the ones provided by the server (from
    // the `assets/` folder).
    rimraf(path.join(createAndGetBuildFolder(), 'css'), () => {
      installDevelopmentWatcher(entryPoint, callback)
    })
  } else {
    installWatcher(entryPoint, callback)
  }
}
function startWatcher (entryPoint, callback) {
  if (config.commands.build.dev) {
    // Delete the assets (CSS/etc.) before.
    // They might not be there, but we must ensure that they are properly
    // deleted.
    //
    // This is necessary, otherwise, remaining copied CSS files will have
    // an higher priority than the ones provided by the server (from
    // the `assets/` folder).
    rimraf(path.join(createAndGetBuildFolder(), 'css'), () => {
      installDevelopmentWatcher(entryPoint, callback)
    })
  } else {
    installWatcher(entryPoint, callback)
  }
}
Start watching files and assets.