alex

var gulp       	 = require('gulp');
var sass       	 = require('gulp-sass');
var browserSync 	 = require('browser-sync').create();
var autoprefixer 	 = require('gulp-autoprefixer');
var plumber 		 = require('gulp-plumber');

gulp.task('browser-sync', function(done) { 
  browserSync.init({
    server: {
      baseDir: './out'
    },
    notify: false
  });
  
  browserSync.watch('out/').on('change', browserSync.reload);
  
  done()
});	

gulp.task('sass', function(done){
  gulp.src('app/scss/*.scss')
    .pipe(plumber({
      errorHandler : function(err) {
        console.log(err);
        this.emit('end');
      }
    }))
    .pipe(sass({errLogToConsole: true}))
    .pipe(sass({outputStyle: 'compact'}))
    .pipe(autoprefixer({
      browsers: ['last 4 versions'],
      cascade: false
    }))
   .pipe(gulp.dest('out/assets/css'))
   .pipe(browserSync.reload({stream: true}));
  
  done()
});

gulp.task('watch', gulp.series('sass', 'browser-sync', function(done) {
  gulp.watch('app/**/*.*', gulp.series('sass'));
  
  done()
}));

function compileJade(done) {
  gulp.src('src/jade/*.jade')
    .pipe(plumber())
    .pipe(jade())
    .pipe(gulp.dest('build/'))
    .pipe(server.reload({ stream: true }));
  
  
  done()
}

function compileScss(done) {
  gulp.src([
    'src/sass/*.scss',
    '!src/sass/mixins.scss',
    '!src/sass/normalize.scss',
    '!src/sass/variable.scss'
  ])
    .pipe(plumber())
    .pipe(sass({ outputStyle: 'compressed' }).on('error', sass.logError))
    .pipe(postcss([
      autoprefixer({
        browsers: [
          "last 1 version",
          "last 2 Chrome versions",
          "last 2 Firefox versions",
          "last 2 Opera versions",
          "last 2 Edge versions"
        ],
        grid: true
      })
    ]))
    .pipe(gcmq())
    .pipe(minify())
    .pipe(gulp.dest('build/css'))
    .pipe(server.reload({ stream: true }));
  
  
  done()
}

function compileScripts(done) {
  gulp.src('src/js/*.js')
    .pipe(plumber())
    .pipe(jsmin())
    .pipe(gulp.dest('build/js/'))
    .pipe(server.reload({ stream: true }));
  
  
  done()
}

function makeHash(done) {
  gulp.src('build/index.html')
    .pipe(hash())
    .pipe(gulp.dest('build'));
  
  
  done()
}

function watcher(done) {
  server.init({
    server: 'build'
  });
  
  gulp.watch('src/sass/**/*.scss', gulp.series(compileScss, makeHash));
  gulp.watch('src/**/*.jade', gulp.series(compileJade, makeHash));
  gulp.watch('src/js/*.js', gulp.series(compileScripts, makeHash));
  
  
  done()
}

module.exports = {
  default: watcher,
  watcher,
  build: gulp.series(
    compileJade,
    compileScss,
    compileScripts,
    makeHash
  ),
  jade: compileJade,
  style: compileScss,
  script: compileScripts,
  hash: makeHash
}

const opacity = document.getElementsByClassName('move-img');

if (opacity.length) {
  // код
}

var gulp = require('gulp');
var browserSync = require('browser-sync').create();
var sass = require('gulp-sass');

gulp.task('sass', function(done) {
    gulp.src("scr/scss/*.scss")
        .pipe(sass())
        .pipe(gulp.dest("scr/css"))
        .pipe(browserSync.stream());


    done();
});

gulp.task('serve', function(done) {

    browserSync.init({
        server: "src/"
    });

    gulp.watch("scr/sass/*.sass", gulp.series('sass'));
    gulp.watch("scr/*.html").on('change', () => {
      browserSync.reload();
      done();
    });
  

    done();
});

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

gulp.task('watch', function() {
  gulp.watch([paths.pug.load[0],paths.pug.load[1]], gulp.series(
    'pug:build',
    done => {
      reload();
      done();
    }
  ));
});

И что за новые возможности series, parallel появились?

эта загадка человечества, разгадать которую можно, прочитав документацию

@custom-media

var $ = require('jquery');
require('jquery-ui/ui/widgets/slider');

$('#id').slider();

var concat = require('concat'); // не gulp-concat
var uglify = require('uglifyjs'); // не gulp-uglifyjs

Посмотрите еще раз внимательно в devDependencies

gulp-rev-replace

const gulp = require('gulp');
const revReplace = require('gulp-rev-replace');

gulp.task('revision', (done) => {
	const manifestFile = gulp.src('path/to/manifest.json');
	
	gulp.src('public/*.html')
		.pipe(revReplace({manifest: manifestFile}))
		.pipe(gulp.dest('public'));

	done();
});