JavaScript is Beautiful (w/ a little ES6 make-up)

ch1.js

// Smart decider
var age = 20;
age >= 18 && console.log( "You are allowed to play this game" ); // TRUE
age >= 18 || console.log( "The game is restricted to 18 and over" ); // FALSE

function fn( cb ) {
  cb && cb();
};

// Configuring a new Object
var task = new Object();
Object.defineProperty(task, 'toString', {
    value: function () {
      return this.title + ' ' + this.description;
    },
    writable: false, // cannot be overwriten
    enumerable: false, // does not get listed using Object.keys()
    configurable: false // 
});

// [INFO] adding `new` in front of a function creates an Object with its own scope (creates a constructor function out of that function). Binds `this` to the new object scope returing.
// Using Prototypes for better memory management
var myObject = function(name){
  this.aValueFromMainObject = false;
}
myObject.prototype.complete = function(){
  console.log('from the proto', this.aValueFromMainObject);
  this.aValueFromMainObject = true;
}

// Using Classes in ES6
'use strict'
class Task {
    constructor(name) {
      this.name = name;
      this.completed = false;
    };
    complete() {
      console.log('completing task: ' + this.name);
      this.completed = true;
    };
    save() {
      console.log('saving Task: ' + this.name);
    };
}

// filter all the array elements greater than 2
// Using an array function, we can do filtering in a cleaner form with ES6:
var res = [ 1, 2, 3, 4 ].filter(function( v ){
  return v > 2;
})
console.log( res ); // [3, 4]
var res = [ 1, 2, 3, 4 ].filter( v => v > 2 );
console.log( res ); // [3,4]

// In ES6 we can get rid of the function keyword and the colon. So the preceding code can be put this way:
let foo = {
  bar ( param1, param2 ) {
  }
}

// ES6 Spread operator
let cb = function( foo, bar, ...args ) {
  console.log( foo, bar, args );
} cb( "foo", "bar", 1, 2, 3); // foo bar [1, 2, 3]

let [ bar, ...others ] = [ "bar", "foo", "baz", "qux" ];
console.log([ bar, others ]); // ["bar",["foo","baz","qux"]]

var data = Array( 5 );
console.log( data.fill( "bar" ) ); // ["bar", "bar", "bar", "bar", "bar"]

var a = [2,3,4];
var b = [ 1, ...a, 5 ];
console.log( b ); // [1,2,3,4,5]

// ForEach keys
var options = {
  bar: "bar",
  foo: "foo"
};
Object.keys( options ).forEach(function( key ){
  console.log( key, options[ key] );
});

// Convert a NodeList to an Array
var nodes = document.querySelectorAll( "div" ),
arr = [].slice.call( nodes );
// or in the ES6 way
arr = Array.from( nodes );

// New default param in ES6
function foo(x = 11, y = 31) { 
  console.log( x + y );
}
function foo(x = y + 3, z = bar( x )) { 
  console.log( x, z );
}

ch2.js

//