Getting Started with Grunt article: set up package.json and uglify task.

Gruntfile.js

module.exports = function(grunt) {
  // This is where our tasks go
  grunt.initConfig({
    pkg: grunt.file.readJSON('package.json'),
    uglify: {
      options: {
        preserveComments: 'some'
      },
      core_dev: {
        options: {
          mangle: false,
          compress: false
        },
        files: [{
          src: 'src/js/core/*.js',
          dest: 'dist/js/core.min.js'
        }]
      },
      core_dist: {
        options: {
          sourceMap: false
        },
        files: [{
          src: 'src/js/core/*.js',
          dest: 'dist/js/core.min.js'
        }]
      },
      extras: {
        options: {
          sourceMap: false
        },
        files: [{
          expand: true,
          cwd: 'src/js',
          src: '*.js',
          dest: 'dist/js',
          ext: '.min.js',
          extDot: 'first'
        }]
      }
    }
  });
  
  // Load tasks from the installed modules
  grunt.loadNpmTasks('grunt-contrib-clean');
  grunt.loadNpmTasks('grunt-contrib-copy');
  grunt.loadNpmTasks('grunt-contrib-sass');
  grunt.loadNpmTasks('grunt-contrib-uglify');
  grunt.loadNpmTasks('grunt-contrib-watch');
  grunt.loadNpmTasks('grunt-focus');
  grunt.loadNpmTasks('grunt-notify');
}

package.json

{
  "name": "my-project-name",
  "version": "0.1.0",
  "private": true,
  "devDependencies": {
    "grunt": "^0.4.5",
    "grunt-contrib-clean": "^0.6.0",
    "grunt-contrib-copy": "^0.7.0",
    "grunt-contrib-sass": "^0.8.1",
    "grunt-contrib-uglify": "^0.7.0",
    "grunt-contrib-watch": "^0.6.1",
    "grunt-focus": "^0.1.1",
    "grunt-notify": "^0.4.1"
  }
}