Hexa's Blog

JavaScript learning

30/04/2015 cheatsheet

1. Function and Variable

a. Declare function

var function_name = function(){
//Do something here
}

b. Declare variable

var variable_name = 123;

c. Reuse method

var function_namedA = function(){
    this.age = 123;
    Console.log(this.age);
}
var Bob = {
    age = 12;
}
Bob.function_namedA();
//The age of Bob changed from 12 to 123

#2. Object a. Make an object

// type 1
var object_name = {
	variable_name1 = 123;
    variable_name2 = 123;
}
// type 2
object  = new Object();
object.variable_name1 = 123;

b. Make constructor of an object

function Person(job, age){
    this.job = job;
    this.age = age;
}

c. Use constructor of an object

var Bob = new Person('engineer', 23);

d. Use variables of an object

//type 1
var a = object[var_name]
//type 2
var a = object.var_name

e. Private and public variables and function

  • private variables are declared with the var keyword inside the object, and can only be accessed by private functions and privileged methods.
  • private functions are declared inline inside the object’s constructor (or alternatively may be defined via var functionName=function(){...}) and may only be called by privileged methods (including the object’s constructor).
  • privileged methods are declared with this.methodName=function(){...} and may invoked by code external to the object.
  • public properties are declared with this.variableName and may be read/written from outside the object.
  • public methods are defined by Classname.prototype.methodName = function(){...} and may be called from outside the object.
  • prototype properties are defined by Classname.prototype.propertyName = someValue
  • static properties are defined by Classname.propertyName = someValue
var Person = function(job, age){
    //job and age are public variables
    this.job = job;
    this.age = age;
	//sex is private variable
	var sex = 'male';
	//printJob() is a public function
    this.printJob(){
	    Console.log(this.job);
	}
	//sayHello() is private function	
	var sayHello = function(){
	    Console.log('Hello');
	}	
}
Person.variable = 123; //variable is pointing to object named Person
Person.prototype.variable = 345; //variable is pointing to the function of object named Person

#3. Inheritance a.Inheritance object

var a = {a: 1}; 
// a ---> Object.prototype ---> null

var b = Object.create(a);
// b ---> a ---> Object.prototype ---> null
console.log(b.a); // 1 (inherited)

var c = Object.create(b);
// c ---> b ---> a ---> Object.prototype ---> null

var d = Object.create(null);
// d ---> null
console.log(d.hasOwnProperty); 
// undefined, because d doesn't inherit from Object.prototype

#4. Notes

  • Keyword this, within a function, this refers to object which call the function.