[10] === 10  // is false
[10] == 10  // is true
'10' == 10   // is true
'10' === 10  // is false
 []  == 0   // is true
 [] === 0   // is false
 '' == false  // is true but true == "a" is false
 '' === false // is false

function Person(firstName, lastName){
  this.firstName = firstName;
  this.lastName = lastName;
}
var Saad = new Person("Saad", "Mousliki");

var arr = ["a", "b", "c"];
typeof arr;  // 返回 "object" 
arr instanceof Array // true
arr.constructor(); //[]

(function(){
  // 置于此处的代码将自动执行
})(); 
(function(a,b){
  var result = a+b;
  return result;
})(10,20)

var items = [12, 548 , 'a' , 2 , 5478 , 'foo' , 8852, , 'Doe' , 2145 , 119];
var randomItem = items[Math.floor(Math.random() * items.length)];

var numbersArray = [] , max = 100;
for( var i=1; numbersArray.push(i++) < max;); // numbers = [1,2,3 ... 100]

function generateRandomAlphaNum(len) {
  var rdmString = "";
  for( ; rdmString.length < len; rdmString += Math.random().toString(36).substr(2));
  return rdmString.substr(0, len);
}

var numbers = [5, 458 , 120 , -215 , 228 , 400 , 122205, -85411];
numbers = numbers.sort(function(){ return Math.random() - 0.5});
/* numbers 数组将类似于 [120, 5, 228, -215, 400, 458, -85411, 122205] */

var array1 = [12 , "foo" , {name "Joe"} , -2458];
var array2 = ["Doe" , 555 , 100];
Array.prototype.push.apply(array1, array2);
/* array1 值为 [12 , "foo" , {name "Joe"} , -2458 , "Doe" , 555 , 100] */

function isNumber(n){
  return !isNaN(parseFloat(n)) && isFinite(n);
}

function isArray(obj){
  return Object.prototype.toString.call(obj) === '[object Array]' ;
}

var myFrame = document.createElement('iframe');
document.body.appendChild(myFrame);
var myArray = window.frames[window.frames.length-1].Array;
var arr = new myArray(a,b,10); // [a,b,10] 
// myArray 的构造器已经丢失，instanceof 的结果将不正常
// 构造器是不能跨 frame 共享的
arr instanceof Array; // false

var numbers = [5, 458 , 120 , -215 , 228 , 400 , 122205, -85411]; 
var maxInNumbers = Math.max.apply(Math, numbers); 
var minInNumbers = Math.min.apply(Math, numbers);

var myArray = [12 , 222 , 1000 ]; 
myArray.length = 0; // myArray will be equal to [].

var items = [12, 548 ,'a' , 2 , 5478 , 'foo' , 8852, , 'Doe' ,2154 , 119 ]; 
items.length; // return 11 
delete items[3]; // return true 
items.length; // return 11 
/* items 结果为 [12, 548, "a", undefined × 1, 5478, "foo", 8852, undefined × 1, "Doe", 2154, 119] */

var items = [12, 548 ,'a' , 2 , 5478 , 'foo' , 8852, , 'Doe' ,2154 , 119 ]; 
items.length; // return 11 
items.splice(3,1) ; 
items.length; // return 10 
/* items 结果为 [12, 548, "a", 5478, "foo", 8852, undefined × 1, "Doe", 2154, 119]

var myArray = [12 , 222 , 1000 , 124 , 98 , 10 ]; 
myArray.length = 4; // myArray will be equal to [12 , 222 , 1000 , 124].

myArray.length = 10; // the new array length is 10 
myArray[myArray.length - 1] ; // undefined

var foo = 10; 
foo == 10 && doSomething(); // is the same thing as if (foo == 10) doSomething(); 
foo == 5 || doSomething(); // is the same thing as if (foo != 5) doSomething();

function doSomething(arg1){ 
  arg1 = arg1 || 10; // arg1 will have 10 as a default value if it's not already set
}

var squares = [1,2,3,4].map(function (val) { 
  return val * val; 
}); 
// squares will be equal to [1, 4, 9, 16]

var num =2.443242342;
num = num.toFixed(4); // num will be equal to 2.4432

0.1 + 0.2 === 0.3 // is false 
9007199254740992 + 1 // is equal to 9007199254740992
9007199254740992 + 2 // is equal to 9007199254740994

for (var name in object) { 
  if (object.hasOwnProperty(name)) { 
    // do something with name
  } 
}

var a = 0; 
var b = ( a++, 99 ); 
console.log(a); // a will be equal to 1 
console.log(b); // b is equal to 99

var navright = document.querySelector('#right'); 
var navleft = document.querySelector('#left'); 
var navup = document.querySelector('#up'); 
var navdown = document.querySelector('#down');

isFinite(0/0) ; // false
isFinite("foo"); // false
isFinite("10"); // true
isFinite(10);  // true
isFinite(undefined); // false
isFinite();  // false
isFinite(null); // true，这点当特别注意

var numbersArray = [1,2,3,4,5];
var from = numbersArray.indexOf("foo") ; // from is equal to -1
numbersArray.splice(from,2);  // will return [5]

var person = {name :'Saad', age : 26, department : {ID : 15, name : "R&D"} };
var stringFromPerson = JSON.stringify(person);
/* stringFromPerson 结果为 "{"name":"Saad","age":26,"department":{"ID":15,"name":"R&D"}}"  */
var personFromString = JSON.parse(stringFromPerson);
/* personFromString 的值与 person 对象相同 */

var func1 = new Function(functionCode);
var func2 = eval(functionCode);

var sum = 0; 
for (var i in arrayNumbers) { 
  sum += arrayNumbers[i]; 
}

var sum = 0; 
for (var i = 0, len = arrayNumbers.length; i < len; i++) { 
  sum += arrayNumbers[i]; 
}

setInterval('doSomethingPeriodically()', 1000); 
setTimeout('doSomethingAfterFiveSeconds()', 5000);

setInterval(doSomethingPeriodically, 1000); 
setTimeout(doSomethingAfterFiveSeconds, 5000);

function getCategory(age) { 
  var category = ""; 
  switch (true) { 
    case isNaN(age): 
      category = "not an age"; 
      break; 
    case (age >= 50): 
      category = "Old"; 
      break; 
    case (age <= 20): 
      category = "Baby"; 
      break; 
    default: 
      category = "Young"; 
      break; 
  }; 
  return category; 
} 
getCategory(5); // 将返回 "Baby"

function clone(object) { 
  function OneShotConstructor(){}; 
  OneShotConstructor.prototype = object; 
  return new OneShotConstructor(); 
} 
clone(Array).prototype ; // []

function escapeHTML(text) { 
  var replacements= {"<": "<", ">": ">","&": "&", "\"": """};           
  return text.replace(/[<>&"]/g, function(character) { 
    return replacements[character]; 
  }); 
}

var object = ['foo', 'bar'], i; 
for (i = 0, len = object.length; i <len; i++) { 
  try { 
    // do something that throws an exception 
  } 
  catch (e) {  
    // handle exception 
  } 
}

var object = ['foo', 'bar'], i; 
try { 
  for (i = 0, len = object.length; i <len; i++) { 
    // do something that throws an exception 
  } 
} 
catch (e) {  
  // handle exception 
}

var xhr = new XMLHttpRequest (); 
xhr.onreadystatechange = function () { 
  if (this.readyState == 4) { 
    clearTimeout(timeout); 
    // do something with response data 
  } 
} 
var timeout = setTimeout( function () { 
  xhr.abort(); // call error callback 
}, 60*1000 /* timeout after a minute */ ); 
xhr.open('GET', url, true); 
xhr.send();

var timerID = 0; 
function keepAlive() { 
  var timeout = 15000; 
  if (webSocket.readyState == webSocket.OPEN) { 
    webSocket.send(''); 
  } 
  timerId = setTimeout(keepAlive, timeout); 
} 
function cancelKeepAlive() { 
  if (timerId) { 
    cancelTimeout(timerId); 
  } 
}

var min = Math.min(a,b); 
A.push(v);

var min = a < b ? a : b; 
A[A.length] = v;