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;
var var2 = 4;

1 / 2; // 0.5
1 / 2 == 1.0 / 2.0; // true

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

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

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

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

var myString = "alpha";

myString += "bet"; //  "alphabet"

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

var x = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9];
var a = [x, x, x, x, x];

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

delete objectName.property;
delete objectName[index];
delete property; // legal only within a with statement

x = 42;
var y = 43;
myobj = new Number();
myobj.h = 4; // create property h
delete x; // returns true (can delete if declared implicitly)
delete y; // returns false (cannot delete if declared with var)
delete Math.PI; // returns false (cannot delete predefined properties)
delete myobj.h; // returns true (can delete user-defined properties)
delete myobj; // returns true (can delete if declared implicitly)

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) {
  // this gets executed
}

typeof operand;
typeof (operand);

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

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

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

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

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

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

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

void expression;
void (expression);

<a href="javascript:void(0)">Click here to do nothing</a>

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

propNameOrNumber in objectName;

// Arrays
var trees = new Array("redwood", "bay", "cedar", "oak", "maple");
0 in trees; // returns true
3 in trees; // returns true
6 in trees; // returns false
"bay" in trees; // returns false (you must specify the index number,
// not the value at that index)
"length" in trees; // returns true (length is an Array property)

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

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

objectName instanceof objectType;

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

this["propertyName"];
this.propertyName;

function validate(obj, lowval, hival) {
  if (obj.value < lowval || obj.value > hival) console.log("Invalid Value!");
}

<p>Enter a number between 18 and 99:</p>
<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]);