var foo = ["one", "two", "three"];

//  
var one = foo[0];
var two = foo[1];
var three = foo[2];

//  
var [one, two, three] = foo;

var var1 = 3,
  var2 = 4;

console.log(1 / 2); /*  0.5 */
console.log(1 / 2 == 1.0 / 2.0); /*  true */

var a1 = true && true; // t && t  true
var a2 = true && false; // t && f  false
var a3 = false && true; // f && t  false
var a4 = false && 3 == 4; // f && f  false
var a5 = "Cat" && "Dog"; // t && t  Dog
var a6 = false && "Cat"; // f && t  false
var a7 = "Cat" && false; // t && f  false

var o1 = true || true; // t || t  true
var o2 = false || true; // f || t  true
var o3 = true || false; // t || f  true
var o4 = false || 3 == 4; // f || f  false
var o5 = "Cat" || "Dog"; // t || t  Cat
var o6 = false || "Cat"; // f || t  Cat
var o7 = "Cat" || false; // t || f  Cat

var n1 = !true; // !t  false
var n2 = !false; // !f  true
var n3 = !"Cat"; // !t  false

console.log("my " + "string"); //      "my string".

var mystring = "alpha";
mystring += "bet"; //   "alphabet"   mystring.

var status = age >= 18 ? "adult" : "minor";

for (var i = 0, j = 9; i <= 9; i++, j--)
  document.writeln("a[" + i + "][" + j + "]= " + a[i][j]);

delete objectName;
delete objectName.property;
delete objectName[index];
delete property; //    with

x = 42;
var y = 43;
myobj = new Number();
myobj.h = 4; //   h
delete x; //  true (    )
delete y; //  false (      var)
delete Math.PI; //  false (   )
delete myobj.h; //  true (   )
delete myobj; //  true (    )

var trees = new Array("redwood", "bay", "cedar", "oak", "maple");
delete trees[3];
if (3 in trees) {
  //   
}

var trees = new Array("redwood", "bay", "cedar", "oak", "maple");
trees[3] = undefined;
if (3 in trees) {
  //    
}

var myFun = new Function("5 + 2");
var shape = "round";
var size = 1;
var today = new Date();

typeof myFun; //  "function"
typeof shape; //  "string"
typeof size; //  "number"
typeof today; //  "object"
typeof dontExist; //  "undefined"

typeof true; //  "boolean"
typeof null; //  "object"

typeof 62; //  "number"
typeof "Hello world"; //  "string"

typeof document.lastModified; //  "string"
typeof window.length; //  "number"
typeof Math.LN2; //  "number"

typeof blur; //  "function"
typeof eval; //  "function"
typeof parseInt; //  "function"
typeof shape.split; //  "function"

typeof Date; //  "function"
typeof Function; //  "function"
typeof Math; //  "object"
typeof Option; //  "function"
typeof String; //  "function"

<a href="javascript:void(0)"> ,    </a>

<a href="javascript:void(document.form.submit())">
   ,    </a
>

// 
var trees = new Array("redwood", "bay", "cedar", "oak", "maple");
0 in trees; //  true
3 in trees; //  true
6 in trees; //  false
"bay" in trees; //  false (    ,
//    )
"length" in trees; //  true (length    Array)

//  
"PI" in Math; //  true
var myString = new String("coral");
"length" in myString; //  true

//  
var mycar = { make: "Honda", model: "Accord", year: 1998 };
"make" in mycar; //  true
"model" in mycar; //  true

var theDay = new Date(1995, 12, 17);
if (theDay instanceof Date) {
  //  
}

function validate(obj, lowval, hival) {
  if (obj.value < lowval || obj.value > hival) alert(" !");
}

<b>   18  99:</b>
<input type="text" name="age" size="3"  />

var a = 1;
var b = 2;
var c = 3;

//  
a + b * c; // 7
//    
a + (b * c); // 7

//      ,
//     
(a + b) * c; // 9

//   
a * c + b * c; // 9

[for (i of [ 1, 2, 3 ]) i*i ];
// [ 1, 4, 9 ]

var abc = [ "A", "B", "C" ];
[for (letters of abc) letters.toLowerCase()];
// [ "a", "b", "c" ]

var objectName = new objectType([param1, param2, ..., paramN]);

super([arguments]); //   . super.functionOnParent([arguments]);

var parts = ["shoulder", "knees"];
var lyrics = ["head", ...parts, "and", "toes"];

function f(x, y, z) {}
var args = [0, 1, 2];
f(...args);