آموزش جاوا اسکریپت Java Script قسمت سوم

 
var length = 16;                                                              // Number
var lastName = "Johnson";                                           // String
var flag = true;                                                                // Boolean
var cars = ["Saab", "Volvo", "BMW"];                        // Array
var x = {firstName:"John", lastName:"Doe"};           // Object
var now = Date();                                                           // Date
var nullVar = null;                                                          // Null
var y;                                                                                // Undefined

 var x;
x = 16; 
x = "Johnson";  
x = true;

 12== 12                //true
12== "12"//true
12=== "12"//false
12=== 12//true

 var x = 999999999999999;  // x will be 999999999999999
var y = 9999999999999999;  // y will be 10000000000000000

var x = 0.2 + 0.1;         // x will be 0.30000000000000004	

 var x =  2 / 0;          // x will be Infinity
var y = -2 / 0;         // y will be –Infinity

 var x =  2 / "apple";// x will be NaN

NaN=== NaN;                            // false
Number.NaN=== NaN;            // false
isNaN(NaN);                               // true
isNaN(Number.NaN);               // true

function valueIsNaN(v) { return v !== v; }
valueIsNaN(1);                           // false
valueIsNaN(NaN);                     // true
valueIsNaN(Number.NaN);     // true

 var x = {firstName:"John", lastName:"Doe"};

 varfirstName = x.firstName;
//or
varfirstName = x["firstName"];

 var arr = new Array();
var str = new String()

 vararr = [];
varstr = "";

 typeof"2.2";     //returns string

 var  x;   //returns   undefined

 undefined == null    //returns true
undefined === null      //returns false	

 var arr = ["Ali", 12, true, myFunction, [1, 2]];