var x; // 聲明 x
console.log(x); //output: undefined 

console.log(typeof y); //output: undefined 

console.log(z); // 拋出異常: ReferenceError: z is not defined

var y = 1;
if (function f(){}) {
  y += typeof f;
}
console.log(y);

var k = 1;
if (1) {
  eval(function foo(){});
  k += typeof foo;
}
console.log(k); 

var k = 1;
if (1) {
  function foo(){};
  k += typeof foo;
}
console.log(k); // output 1function

var Employee = function (name, company, salary) {
  this.name = name || "";    
  this.company = company || ""; 
  this.salary = salary || 5000; 

  // Private method
  var increaseSalary = function () {
    this.salary = this.salary + 1000;
  };

  // Public method
  this.dispalyIncreasedSalary = function() {
    increaseSlary();
    console.log(this.salary);
  };
};

// Create Employee class object
var emp1 = new Employee("John","Pluto",3000);
// Create Employee class object
var emp2 = new Employee("Merry","Pluto",2000);
// Create Employee class object
var emp3 = new Employee("Ren","Pluto",2500);

var globalVar = "abc"; 

// Parent self invoking function 
(function outerFunction (outerArg) { // begin of scope outerFunction
  // Variable declared in outerFunction function scope 
  var outerFuncVar = 'x';  
  // Closure self-invoking function 
  (function innerFunction (innerArg) { // begin of scope innerFunction
    // variable declared in innerFunction function scope
    var innerFuncVar = "y"; 
    console.log(     
      "outerArg = " + outerArg + "n" +
      "outerFuncVar = " + outerFuncVar + "n" +
      "innerArg = " + innerArg + "n" +
      "innerFuncVar = " + innerFuncVar + "n" +
      "globalVar = " + globalVar);
 
  }// end of scope innerFunction)(5); // Pass 5 as parameter 
}// end of scope outerFunction )(7); // Pass 7 as parameter 
innerFunction is closure that is defined inside outerFunc

console.log(mul(2)(3)(4)); // output : 24 
console.log(mul(4)(3)(4)); // output : 48

function mul (x) {
  return function (y) { // anonymous function 
    return function (z) { // anonymous function 
      return x * y * z; 
    };
  };
}

var arrayList = ['a','b','c','d','e','f'];

arrayList = [];

arrayList.length = 0;

arrayList.splice(0, arrayList.length);

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

function isArray(obj){
  return obj.__proto__ === Array.prototype;
}

function isArray(obj){
  return $.isArray(obj)
}

var output = (function(x){
  delete x;
  return x;
})(0);
 
console.log(output);

var x = 1;
var output = (function(){
  delete x;
  return x;
})();

console.log(output);

var x = { foo : 1};
var output = (function(){
  delete x.foo;
  return x.foo;
})();

console.log(output);

var Employee = {
  company: 'xyz'
}
var emp1 = Object.create(Employee);
delete emp1.company
console.log(emp1.company);

var trees = ["redwood","bay","cedar","oak","maple"];
delete trees[3];
console.log(trees);

var trees = ["xyz","xxxx","test","ryan","apple"];
delete trees[3];
 
console.log(trees.length);

var bar = true;
console.log(bar + 0);  
console.log(bar + "xyz"); 
console.log(bar + true); 
console.log(bar + false);  

var z = 1, y = z = typeof y;
console.log(y); 

var z = 1
z = typeof y;
var y = z;
console.log(y); 

var foo = function bar(){ return 12; };
typeof bar(); 

var bar = function(){ return 12; };
typeof bar(); 

function bar(){ return 12; };
typeof bar(); 

var foo = function bar(){ 
  // foo is visible here 
  // bar is visible here
  console.log(typeof bar()); // Work here :)
};
// foo is visible here
// bar is undefined here

var foo = function(){ 
  // Some code
}; 
function bar(){ 
  // Some code
}; 

console.log(foo)
console.log(bar)

var foo = function(){ 
  // Some code
}; 
function bar(){ 
  // Some code
}; 

undefined
function bar(){ 
  // Some code
}; 

// foo bar的定義位置被提升
function bar(){ 
  // Some code
}; 
var foo;

console.log(foo)
console.log(bar)

foo = function(){ 
  // Some code
}; 

var salary = "1000$";

(function () {
  console.log("Original salary was " + salary);

  var salary = "5000$";

  console.log("My New Salary " + salary);
})();

var salary = "1000$";

 (function () {
   var salary ;
   console.log("Original salary was " + salary);

   salary = "5000$";

   console.log("My New Salary " + salary);
 })();

function foo(){ 
 return foo; 
}

console.log(new foo() instanceof foo);

function Animal(){
  //或者不寫return語(yǔ)句
  return this;
}
var dog = new Animal();
dog instanceof Animal // Output : true

function foo(){ 
 return foo; 
}

// here bar is pointer to function foo(){return foo}.
var bar = new foo();

var counterArray = {
  A : 3,
  B : 4
};
counterArray["C"] = 1;

Object.keys(counterArray).length // Output 3