es6.js

"use strict";

function func1() {
  if (true) {
      let tmp = 123;
  }
  console.log("func1 tmp", tmp); // ReferenceError: tmp is not defined
}
func1();

// In contrast, var-declared variables are function-scoped:

function func2() {
  if (true) {
      var tmp = 123;
  }
  console.log("func2 tmp", tmp); // 123
}
func2();

// Block scoping means that you can shadow variables within a function:

function func3() {
  var foo = 5;
  if (true) {
     var foo = 10;
  }
  console.log("func3 with var", foo);
}
func3();

function func4() {
  let foo = 5;
  if (true) {
     let foo = 10; // shadows outer `foo`
     console.log(foo); // 10
  }
  console.log("func4 4 with let", foo); // 5
}
func4();

const MAX_CAT_SIZE_KG = 3000;
MAX_CAT_SIZE_KG = 5000; // SyntaxError

console.log("MAX_Cat", MAX_CAT_SIZE_KG );

// ***************Arrow functions*******************

var reflect = function(value) {
    return value;
};

console.log("reflect in ES5: ", reflect("ES5 is so yesterday.") );

// effectively equivalent to:

var reflect = value => value;

console.log("reflect in ES6: ", reflect("ES6 is the new hotness.") );

// With more than one arg you need parens
var sum = (num1, num2) => num1 + num2;

// effectively equivalent to:

var sum = function(num1, num2) {
    return num1 + num2;
};

// With no args, you need an empty parens
var sum = () => 1 + 2;

// effectively equivalent to:

var sum = function() {
    return 1 + 2;
};

// ******************Object Literal Property Value Shorthand****************
let wow = "Hi there",
    es6 = "ES6",
    myNum = function(){console.log("howdy");};

var myOldObj = {
  wow: wow,
  es6: es6,
  myNum: myNum
}

// console.log("myOldObj", myOldObj );

var myNewObj = {
  wow, es6, myNum
}

console.log("my New Obj", myNewObj.myNum );
myNewObj.myNum();