如何实现使用gulp实现文件压缩及浏览器的热加载

var gulp = require('gulp');var sass = require('gulp-sass');var browserSync = require('browser-sync');var uglify = require('gulp-uglify');var imagemin = require('gulp-imagemin');var minifyCSS  = require('gulp-minify-css');var cache = require('gulp-cache');var del = require('del');var runSequence = require('run-sequence');var minifyHtml= require("gulp-minify-html");

gulp.task('sass', function(){   //打包sass
  return gulp.src('app/scss/**/*.scss')
    .pipe(sass()) // Converts Sass to CSS with gulp-sass.pipe(gulp.dest('app/css'))
    .pipe(browserSync.reload({
      stream: true}))
});

gulp.task('js',function() {

    gulp.src('app/**/*.js')

    .pipe(uglify())//压缩.pipe(gulp.dest('dist'));

});

gulp.task('css', function () {
    gulp.src('app/css/*.css')
    .pipe(minifyCSS())
    .pipe(gulp.dest('dist/css'))
})

gulp.task('minify-html',function() {

      gulp.src('app/**/*.html')//要压缩的html文件 .pipe(gulp.dest('dist'));

});


gulp.task('images', function(){  return gulp.src('app/images/**/*.+(png|jpg|jpeg|gif|svg)')  // Caching images that ran through imagemin  .pipe(cache(imagemin({
      interlaced: true})))
  .pipe(gulp.dest('dist/images'))
});

gulp.task('clean', function(callback) {
  del('dist');  return cache.clearAll(callback);
});

gulp.task('watch',['browserSync', 'sass'],function(){   //我们可以在watch任务之前告知Gulp，先把browserSync和Sass任务执行了再说。
  gulp.watch('app/scss/**/*.scss', ['sass']);
  gulp.watch('app/*.html', browserSync.reload);
  gulp.watch('app/js/**/*.js', browserSync.reload);  // Other watchers});

gulp.task('browserSync', function() {  //浏览器热加载  browserSync({
    server: {
      baseDir: 'app'},
  })
});

gulp.task('build', function (callback) {
  runSequence('clean',['minify-html','js','images','css'],callback)
});

gulp.task('default', function (callback) {
  runSequence(['sass','browserSync', 'watch'],
    callback
  )
});