gulp-useref不会影响我的js，它只是在级联

Question

Gulp useref uglify（）不会缩小js文件，它只能进行串联。

预期结果将所有文件连接到一个文件并缩小文件。

            <!-- build:css css/combined.css -->
            <link rel="stylesheet" href="css/style1.css" type="text/css">
            <link rel="stylesheet" href="css/style2.css" type="text/css">
            <link rel="stylesheet" href="css/style3.css" type="text/css">
            <!-- endbuild -->
            <!-- build:js scripts/combinedlib.js -->
            <script src="js/script1.js"></script>
            <script src="js/script2.js"></script>
            <script src="js/script3.js"></script>
            <script src="js/script4.js"></script>
            <!-- endbuild -->
            <!-- build:js scripts/app.js -->
            <script src="scripts/app.js"></script>
            <!-- endbuild -->
            <!-- build:js scripts/config.js -->
            <script src="config/config1.js"></script>
            <script src="config/config2.js"></script>
            <script src="config/config3.js"></script>
            <script src="config/config4.js"></script>
            <!-- endbuild -->
            <!-- build:js scripts/common.js -->
            <script src="config/common1.js"></script>
            <script src="config/common2.js"></script>
            <script src="config/common3.js"></script>
            <script src="config/common4.js"></script>
            <!-- endbuild -->

预期结果：以下所有文件都必须缩小。 组合lib.js，app.js，config.js，common.js

我的Gulp文件

            var gulp = require('gulp'),
            useref = require('gulp-useref'),
            gulpif = require('gulp-if'),
            del = require('del');
            uglify = require('gulp-uglify'),
            minifyCss = require('gulp-clean-css'),
            replace = require('gulp-replace'),
            rename = require('gulp-rename');
            gulp.task('clean', function () {
                return del('dist/');
            });
            gulp.task('buildapp', function () {
                 gulp.src("app/images/**/*.*")
                  .pipe(gulp.dest('dist/images/'));
                 gulp.src("app/css/fonts/*.*")
                  .pipe(gulp.dest('dist/fonts/'));
                 gulp.src("app/modules/**/*.html")
                  .pipe(gulp.dest('dist/modules/'));
                 gulp.src("app/modules/**/*.json")
                  .pipe(gulp.dest('dist/modules/'));

               return gulp.src('app/index.html')
                .pipe(useref())
                .pipe(gulpif('app/**/*.js', uglify()))
                .pipe(gulpif('app/assets/**/*.css', minifyCss()))
                .pipe(gulpif("app/images/**/*.*",gulp.dest('dist/images') ))
                .pipe(gulp.dest('dist'));
            }); 
        gulp.task('default', gulp.series('clean','buildapp'));