Gulp error in the console - gulp

Question

I use Gulp 4 and get following error in the console ( I tried to upgrade the gulpfile code to gulp 4, but it's still not working):
$ gulp
[13:30:25] Using gulpfile c:\Users\Sylwia Szymańska\Projects\New project\gulpfil
e.js
[13:30:25] Starting 'default'...
[13:30:25] 'default' errored after 2.95 ms
[13:30:25] AssertionError: Task function must be specified
at Gulp.set [as _setTask] (C:\Users\user\Projects\New project\no
de_modules\undertaker\lib\set-task.js:10:3)
at Gulp.task (C:\Users\user\Projects\New project\node_modules\un
dertaker\lib\task.js:13:8)
at C:\Users\user\Projects\New project\node_modules\gulp-series\l
ib\gulp-series.js:27:11
at Array.forEach (native)
at C:\Users\user\Projects\New project\node_modules\gulp-series\l
ib\gulp-series.js:23:11
at taskWrapper (C:\Users\user\Projects\New project\node_modules\
undertaker\lib\set-task.js:13:15)
at bound (domain.js:280:14)
at runBound (domain.js:293:12)
at asyncRunner (C:\Users\user\Projects\New project\node_modules\
async-done\index.js:36:18)
at _combinedTickCallback (internal/process/next_tick.js:67:7)
My gulpfile:
var gulp = require('gulp');
var build = require('gulp-build');
var sass = require('gulp-sass');
var sourcemaps = require('gulp-sourcemaps');
var browser_sync = require('browser-sync');
var gulps = require("gulp-series");
var watch = require('gulp-watch');
var less = require('gulp-less');
var livereload = require('gulp-livereload');
gulp.task('stream', function () {
// Endless stream mode
return watch('css/**/*.css', { ignoreInitial: false })
.pipe(gulp.dest('build'));
});
gulp.task('callback', function () {
// Callback mode, useful if any plugin in the pipeline depends on the `end`/`flush` event
return watch('css/**/*.css', function () {
gulp.src('css/**/*.css')
.pipe(gulp.dest('build'));
});
});
gulp.task('build', function() {
gulp.src('scripts/*.js')
.pipe(build({ GA_ID: '123456' }))
.pipe(gulp.dest('dist'))
});
'use strict';
var gulp = require('gulp');
var sass = require('gulp-sass');
gulp.task('sass', function () {
return gulp.src('./sass/**/*.scss')
.pipe(sass().on('error', sass.logError))
.pipe(gulp.dest('./css'));
});
gulp.task('sass:watch', function () {
gulp.watch('./sass/**/*.scss', ['sass']);
});
//sourcemaps???
var gulp = require('gulp');
// var plugin1 = require('gulp-plugin1');
// var plugin2 = require('gulp-plugin2');
var sourcemaps = require('gulp-sourcemaps');
gulp.task('javascript', function() {
gulp.src('src/**/*.js')
.pipe(sourcemaps.init())
// .pipe(plugin1())
// .pipe(plugin2())
.pipe(sourcemaps.write())
.pipe(gulp.dest('dist'));
});
// var less = require('gulp-less'),
// livereload = require('gulp-livereload');
gulp.task('less', function() {
gulp.src('less/*.less')
.pipe(less())
.pipe(gulp.dest('css'))
.pipe(livereload());
});
gulp.task('watch', function() {
livereload.listen();
gulp.watch('less/*.less', ['less']);
});
var gulps = require("gulp-series");
gulps.registerTasks({
"test1" : (function(done) {
setTimeout(function() {
console.log("test1 is done");
done();
}, 1000);
}),
"test2" : (function() {
console.log("test2 is done");
})
});
gulps.registerSeries("default", ["test1", "test2"]);
var concat = require('gulp-concat');
gulp.task('scripts', function() {
return gulp.src('./lib/*.js')
.pipe(concat('all.js'))
.pipe(gulp.dest('./dist/'));
});
I'll be gratefull for help!
I installed all the packages (I hope, so).

Answer 1

In Gulp 4.0 the gulp.watch task does not accept array arguments like ['sass'] anymore.
You can use gulp.series or gulp.parallel to define the tasks to be executed when gulp.watch triggers a change event.
gulp.task('sass:watch', function () {
gulp.watch('./sass/**/*.scss', gulp.series('sass'));
});
The Complete-Ish Guide to Upgrading to Gulp 4 may be useful.