Gulp 4 - gulp.watch fix (done callback)

gulpfile.js

// This tricks prevents the reload-only-once 'new' feature
// of Gulp 4, when using gulp.watch

'use strict';

var gulp     = require('gulp'),
    sass     = require('gulp-sass'),
    electron = require('electron-connect').server.create();

// You should also add a 'clean' task to clean the dist folder
// I removed it because it is not needed in this example

gulp.task('serve', function () {
  electron.start();
  gulp.watch('app/**/*.sass', gulp.series('styles', reload)); // <-- The trick is here, you need to create function with the done callback
  // Here are some more examples in case you're not sure:
  //gulp.watch('app/**/*.pug', gulp.series('views', reload));
  //gulp.watch('app/**/*.ts', gulp.series('scripts', reload));
});

// See? Simple.
function reload(done) {
  electron.reload();
  done();
}

gulp.task('default', gulp.series('styles', 'serve'));

Thanks - i "simplified" it even a bit more using an arrow function:

gulp.watch('app/**/*.sass', gulp.series('styles', done => {
  electron.reload();
  done();
}));