let

function varTest() {
  var x = 1;
  if (true) {
    var x = 2; //   !
    console.log(x); // 2
  }
  console.log(x); // 2
}

function letTest() {
  let x = 1;
  if (true) {
    let x = 2; //  
    console.log(x); // 2
  }
  console.log(x); // 1
}

var list = document.getElementById("list");

for (let i = 1; i <= 5; i++) {
  let item = document.createElement("li");
  item.appendChild(document.createTextNode("Item " + i));

  item.onclick = function (ev) {
    console.log("Item " + i + " is clicked.");
  };
  list.appendChild(item);
}

//        'var'
//    
//  ,    
for (var i = 1; i <= 5; i++) {
  var item = document.createElement("li");
  item.appendChild(document.createTextNode("Item " + i));

  (function (i) {
    item.onclick = function (ev) {
      console.log("Item " + i + " is clicked.");
    };
  })(i);
  list.appendChild(item);
}

var x = "global_x";
let y = "global_y";
console.log(this.x); // 'global_x'
console.log(this.y); // undefined

var SomeConstructor;

{
  let privateScope = {};

  SomeConstructor = function SomeConstructor() {
    this.someProperty = "foo";
    privateScope.hiddenProperty = "bar";
  };

  SomeConstructor.prototype.showPublic = function () {
    console.log(this.someProperty); // foo
  };

  SomeConstructor.prototype.showPrivate = function () {
    console.log(privateScope.hiddenProperty); // bar
  };
}

var myInstance = new SomeConstructor();

myInstance.showPublic();
myInstance.showPrivate();

console.log(privateScope.hiddenProperty); // error

if (x) {
  let foo;
  let foo; // SyntaxError thrown.
}

function do_something() {
  console.log(bar); // undefined
  console.log(foo); // ReferenceError: foo is not defined
  var bar = 1;
  let foo = 2;
}

switch (x) {
  case 0:
    let foo;
    break;

  case 1:
    let foo; //  SyntaxError -   
    break;
}

var i = 0;
for (let i = i; i < 10; i++) {
  console.log(i);
}

for (let expr1; expr2; expr3) statement;

var a = 5;
var b = 10;

if (a === 5) {
  let a = 4; // The scope is inside the if-block
  var b = 1; // The scope is inside the function

  console.log(a); // 4
  console.log(b); // 1
}

console.log(a); // 5
console.log(b); // 1

for (let i = 0; i < 10; i++) {
  console.log(i); // 0, 1, 2, 3, 4 ... 9
}

console.log(i); // i is not defined

let (var1 [= value1] [, var2 [= value2]] [, ..., varN [= valueN]]) block;

var x = 5;
var y = 0;

let (x = x+10, y = 12) {
  console.log(x+y); // 27
}

console.log(x + y); // 5

var a = 5;
let(a = 6) console.log(a); // 6
console.log(a); // 5

let (decls) expr