gulp.watch doesn't work. What's wrong?

Question

gulp.js

Started learning gulp. I ran into a problem when running the watch task to track changes to style files.

var gulp = require('gulp'),
  sass = require('gulp-sass');

gulp.task('sass', function() {
  return gulp.src('app/sass/main.sass')
  .pipe(sass())
  .pipe(gulp.dest('app/css'))
});

gulp.task("watch", function() {
  gulp.watch('app/sass/main.sass', ['sass']);
});

I run the task, I get an error: Error: watching app/sass/main.sass: watch task has to be a function (optionally generated by using gulp.parallel or gulp.series)
Please help me figure it out.

Answer 1

The error is that you probably have Gulp version 4 installed using the gulp.parallel function, while this gulpfile configuration is for Gulp version 3. The easiest way is to rollback Gulp version to 3.9.1, or fix gulpfile. js:

gulp.task("watch", function() {
  gulp.watch('app/sass/main.sass', gulp.parallel('sass'));
});