Gulpfile.js doesn't work watch, what's wrong?

Question

gulp.js

I compile scss to css using Gulp. Everything was great, but when I started a new project, I found that the Gulpfile.js code, which worked from project to project, stopped working.

'use strict';
 
var gulp = require('gulp');
var sass = require('gulp-sass');
var autoprefixer = require('gulp-autoprefixer');
 
gulp.task('sass', function () {
  gulp.src('./assets/scss/*.scss')
    .pipe(sass().on('error', sass.logError))
    .pipe(sass({outputStyle: 'compressed'}))
    .pipe(autoprefixer({
      browsers: ["last 50 versions", "ie >= 9"],
      cascade: false
  }))
    .pipe(gulp.dest('./assets/css'))
    
});

gulp.task('watch', function () {
  gulp.watch('./assets/scss/*.scss', ['sass']);
});

When I start watch, after changing scss the script works, but nothing happens after starting 'sass'. If you run 'sass', then the console responds

The following tasks did not complete: sass
Did you forget to signal async completion?.

Googling, I found information about gulp.parallel and series in Gulp v4, but did not understand what was happening. Please help

Answer 1

The fourth version introduced a syntax that allows you to specify the order in which tasks are started.
Try like this.

gulp.task('watch', function() {
    gulp.watch('./assets/scss/*.scss',  gulp.series('sass'));
});

here is the video . It details what has changed and why.