• let – block scope; no hoisting
• const
• Blocked scoped functions

  {
      function foo () { return 1 }
      foo() === 1
      {
          function foo () { return 2 }
          foo() === 2
      }
      foo() === 1
  }
  

• Destructuring

  let foo = ["one", "two", "three"];
  
  let [one, two, three] = foo;
  console.log(one); // "one"
  console.log(two); // "two"
  console.log(three); // "three"
  
  //swapping
  let a = 1;
  let b = 3;
  [a, b] = [b, a];
  console.log(a); // 3
  console.log(b); // 1
  
  
  var expense = {
    type: 'Business',
    amount: '$40'
  }
  const {type, amount} = expense;
  
  //Or use in functions:
  function({type, amount}){}
  
  

• Defaults

  let hasDefaults = function(something = "default"){
  console.log(something); //default
  }
  

• Rest/Spread

  Rest:
  function sortRestArgs(...theArgs) {
    var sortedArgs = theArgs.sort();
    return sortedArgs;
  }
  
  console.log(sortRestArgs(5,3,7,1)); // shows 1,3,5,7
  
  Spread:
  const defaultColors = ['red', 'green'];
  const extraColors = ['orange', 'blue'];
  
  [...defaultColors, ...extraColors]
  
  

• Template literals

  var a = 5;
  var b = 10;
  console.log(`Fifteen is ${a + b} and\nnot ${2 * a + b}.`);
  // "Fifteen is 15 and
  // not 20."
  

• Arrow Functions

  let add = (a,b) => a+b;
  let sum = add(1,2);
  

  Also makes ‘this’ behave as you would expect it to behave.

• Iterators and Generators

  for(let value of ["a", "b", "c"]){
      console.log(value)
  }
  // "a"
  // "b"
  // "c"
  
  function* idMaker(){
    var index = 0;
    while(true)
      yield index++;
  }
  var gen = idMaker();
  
  console.log(gen.next().value); // 0
  console.log(gen.next().value); // 1
  console.log(gen.next().value); // 2
  //Or
  for(let value of idMaker()){
      console.log(value)
  }
  
  

• New Data Types

  var myMap = new Map();
  myMap.set(0, "zero");
  myMap.set(1, "one");
  for (var [key, value] of myMap) {
    console.log(key + " = " + value);
  }
  // Will show 2 logs; first with "0 = zero" and second with "1 = one"
  
  
  var mySet = new Set();
  mySet.add(1);
  mySet.add(5);
  mySet.add("some text");
  var o = {a: 1, b: 2};
  mySet.add(o);
  
  mySet.has(1); // true
  mySet.has(3); // false, 3 has not been added to the set
  mySet.has(5);              // true
  mySet.has(Math.sqrt(25));  // true
  mySet.has("Some Text".toLowerCase()); // true
  mySet.has(o); // true
  
  mySet.size; // 4
  
  mySet.delete(5); // removes 5 from the set
  mySet.has(5);    // false, 5 has been removed
  
  var wm1 = new WeakMap(),
      wm2 = new WeakMap(),
      wm3 = new WeakMap();
  var o1 = {},
      o2 = function(){},
      o3 = window;
  
  wm1.set(o1, 37);
  wm1.set(o2, "azerty");
  wm2.set(o1, o2); // a value can be anything, including an object or a function
  wm2.set(o3, undefined);
  wm2.set(wm1, wm2); // keys and values can be any objects. Even WeakMaps!
  
  ar ws = new WeakSet();
  var obj = {};
  var foo = {};
  
  ws.add(window);
  ws.add(obj);
  
  ws.has(window); // true
  ws.has(foo);    // false, foo has not been added to the set
  
  ws.delete(window); // removes window from the set
  ws.has(window);    // false, window has been removed
  
  

• Modules

  //a.js:
  export let a ={};
  export let b =function(){};
  
  //c.js:
  import {a,b} from c
  

• Promises

      var p1 = new Promise(        
          function(resolve, reject) {
              window.setTimeout(
                  function() {
                      resolve(42);
                  }, Math.random() * 2000 + 1000);
          });   
      p1.then(
          function(val) {           
          })
      .catch(
          function(reason) {
              console.log('Handle rejected promise ('+reason+') here.');
          });
  
  //With fetch:
  fetch(url)
    .then(response => response.json())
    .then(data => console.log(data));
  

• Class, constructors

class Test {
  constructor({someProperty}){}
  method(){}
}

class SubTest extends Test{
  constructor(options){
    super(options);
  }
  subMethod(){}
}

• Array Helper methods

  forEach
  map
  filter
  find
  every
  some
  reduce
  

  Examples:

  let colors = ['red', 'blue', 'green'];
  colors.forEach(c => console.log(c)); 
  
  let numbers = [1, 2, 3];
  let doubled = numbers.map(c => c * 2);
  let sum = numbers.reduce((sum, number) => sum + number, 0)
  
  let divisibleByTwo = numbers.filter(c => c % 2 === 0);
  let allDivisibleByTwo= numbers.every(c => c % 2 === 0);
  let someDivisibleByTwo= numbers.some(c => c % 2 === 0);
  
  
  let users = [ {name: 'Jay'},{name: 'May'},{name: 'Jay'} ]
  let jay = users.find(u => u.name === 'Jay')
  
  

• Enhanced Object Literals

  function test(someValue)
  	{
      return {
        someValue: somevalue,
        someFunction: function(){}
   }
  
  Is now equivalent to 
    
   function test(someValue)
  	{
      return {
        someValue,
        someFunction(){}
   }
  
  
  

Some great resources on es6 – https://developer.mozilla.org and http://es6-features.org/