How to minify multiple Javascript files in a folder with UglifyJS?

If you're on Linux/Mac and have access to bash, you can use uglifyjs on multiple JS files like so:

rm *.min.js; for f in *.js; do short=${f%.js}; uglifyjs $f > $short.min.js; done

Further to the above answer, I now have this set up in my .bashrc file:

alias minify='rm *.min.js; for f in *.js; do short=${f%.js}; uglifyjs $f > $short.min.js; done'

npm-only way:

1. run:

   npm install uglifyjs-folder --save-dev
   

2. and afterwards add to your package.json something like:

   "uglifyjs": "uglifyjs-folder js -eo jsm"
   

3. then run:

    npm run uglifyjs
   

Please note, if you'd need to generate to the same folder as the source files are (js), following should do the job:

1. run:

   npm install del-cli uglifyjs-folder --save-dev
   

2. and afterwards add to your package.json something like:

   "uglifyjs": "del js/*.min.js; uglifyjs-folder js -eo js"
   

3. then run:

    npm run uglifyjs
   

I know it might seem like a huge step but I would really recommend using grunt. It's really simple once you get the hang of it.

Here's a crash course:

1. Install NodeJS

2. Install Grunt CLI (just enter this in console/terminal):

   npm install -g grunt-cli
   

3. Create a simple package.json file in the root of your project:

   {
     "name": "my-project-name",
     "version": "1.0.0",
     "devDependencies": {
       "grunt": "~0.4.2",
       "grunt-contrib-uglify": "~0.2.4",
       "grunt-contrib-watch" : "~0.5.3"
     }
   }
   

4. Once you have that, just type: npm install to the console (in the root of your project). This will install the necessary grunt plugins/dependencies (from the package file above).

5. Now create a simple gruntfile.js in the root of your project (it's a kind of config for your project):

   module.exports = function (grunt) {
       grunt.initConfig({
   
       // define source files and their destinations
       uglify: {
           files: { 
               src: 'js/*.js',  // source files mask
               dest: 'jsm/',    // destination folder
               expand: true,    // allow dynamic building
               flatten: true,   // remove all unnecessary nesting
               ext: '.min.js'   // replace .js to .min.js
           }
       },
       watch: {
           js:  { files: 'js/*.js', tasks: [ 'uglify' ] },
       }
   });
   
   // load plugins
   grunt.loadNpmTasks('grunt-contrib-watch');
   grunt.loadNpmTasks('grunt-contrib-uglify');
   
   // register at least this one task
   grunt.registerTask('default', [ 'uglify' ]);
   
   
   };
   

6. Once that's done you just need to build it. Type in the console:

   grunt
   

   or - better - if you type execute the command below - grunt will monitor your source files for changes, and if you change any of them - it will build them automatically:

   grunt watch --force
   

You can then add more plugins, like: css minification, css preprocessors (less, sass, stylus), jshint, etc.