Bundling and minification of ES6 javascript files in an asp.net MVC web application

1. Install BuildBundlerMinifier NuGet package to your project.
2. Add a package.json file, with the following devDependencies, to the root of your project:

{
  "name": "YourProjectName",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "devDependencies": {
    "del": "^3.0.0",
    "gulp": "^4.0.0",
    "gulp-concat": "^2.6.1",
    "gulp-cssmin": "^0.2.0",
    "gulp-htmlmin": "^3.0.0",
    "gulp-terser": "^1.4.0",
    "gulp-uglify": "^3.0.0",
    "merge-stream": "^1.0.1"
  },
  "keywords": [],
  "author": "",
  "license": "ISC"
}

3. Run the following npm commands inside your project root:

npm i

npm i -g gulp-cli

4. Add the following gulpfile.js file below to the project root:

'use strict';

var gulp = require('gulp'),
    concat = require('gulp-concat'),
    cssmin = require('gulp-cssmin'),
    htmlmin = require('gulp-htmlmin'),
    uglify = require('gulp-uglify'),
    merge = require('merge-stream'),
    del = require('del'),
    bundleconfig = require('./bundleconfig.json');
const terser = require('gulp-terser');

const regex = {
    css: /\.css$/,
    html: /\.(html|htm)$/,
    js: /\.js$/
};

gulp.task('min:js', async function () {
    merge(getBundles(regex.js).map(bundle => {
        return gulp.src(bundle.inputFiles, { base: '.' })
            .pipe(concat(bundle.outputFileName))
            //.pipe(uglify())
            .pipe(terser())
            .pipe(gulp.dest('.'));
    }))
});

gulp.task('min:css', async function () {
    merge(getBundles(regex.css).map(bundle => {
        return gulp.src(bundle.inputFiles, { base: '.' })
            .pipe(concat(bundle.outputFileName))
            .pipe(cssmin())
            .pipe(gulp.dest('.'));
    }))
});

gulp.task('min:html', async function () {
    merge(getBundles(regex.html).map(bundle => {
        return gulp.src(bundle.inputFiles, { base: '.' })
            .pipe(concat(bundle.outputFileName))
            .pipe(htmlmin({ collapseWhitespace: true, minifyCSS: true, minifyJS: true }))
            .pipe(gulp.dest('.'));
    }))
});

gulp.task('min', gulp.series(['min:js', 'min:css', 'min:html']));

gulp.task('clean', () => {
    return del(bundleconfig.map(bundle => bundle.outputFileName));
});

gulp.task('watch', () => {
    getBundles(regex.js).forEach(
        bundle => gulp.watch(bundle.inputFiles, gulp.series(["min:js"])));

    getBundles(regex.css).forEach(
        bundle => gulp.watch(bundle.inputFiles, gulp.series(["min:css"])));

    getBundles(regex.html).forEach(
        bundle => gulp.watch(bundle.inputFiles, gulp.series(['min:html'])));
});

const getBundles = (regexPattern) => {
    return bundleconfig.filter(bundle => {
        return regexPattern.test(bundle.outputFileName);
    });
};

gulp.task('default', gulp.series("min"));

5. Inside your .csproj file of your project add the following build task:

<Target Name="MyPreCompileTarget" BeforeTargets="Build">   
  <Exec Command="gulp min" />
 </Target>

6. Add the following bundleconfig.json file below to the project root(here you can add js, css files need to be minified):

[
  {
    "outputFileName": "Content/css/site.min.css",
    "inputFiles": [
      "Content/css/site.css"
    ]
  },
  {
    "outputFileName": "Content/js/site.min.js",
    "inputFiles": [
      "Content/js/site.js"
    ],
    "minify": {
      "enabled": true,
      "renameLocals": true
    },
    "sourceMap": false
  }
]

7. Inside your BundleConfig.cs you can do the following:

   public class BundleConfig
   {
       public static void RegisterBundles(BundleCollection bundles)
     {
   
   
        bundles.Add(new Bundle("~/Content/css/site").Include(
                 "~/Content/css/site.css"));
   
   
        bundles.Add(new ScriptBundle("~/bundles/jquery").Include(
                    "~/Content/lib/jquery/jquery-{version}.js"));
   
        //use Bundle instead of ScriptBundle
        bundles.Add(new Bundle("~/Content/js/site").Include(
                    "~/Content/js/site.js"));
   
        //disable it for development environment
        if (Environment.Development)
        {
            BundleTable.EnableOptimizations = false;
        }
        else
        {
            BundleTable.EnableOptimizations = true;
        }
    }
   }
   

8. Finally inside your view:

   @Styles.Render("~/Content/css/site")
   @Scripts.Render("~/Content/js/site")
   

My answer based on the following MSDN resources:

Bundling and Minification

Bundle and minify static assets in ASP.NET Core