Which way is best for creating an object in JavaScript? Is `var` necessary before an object property?

Solution 1:

There is no best way, it depends on your use case.

• Use way 1 if you want to create several similar objects. In your example, Person (you should start the name with a capital letter) is called the constructor function. This is similar to classes in other OO languages.
• Use way 2 if you only need one object of a kind (like a singleton). If you want this object to inherit from another one, then you have to use a constructor function though.
• Use way 3 if you want to initialize properties of the object depending on other properties of it or if you have dynamic property names.

Update: As requested examples for the third way.

Dependent properties:

The following does not work as this does not refer to book. There is no way to initialize a property with values of other properties in a object literal:

var book = {
    price: somePrice * discount,
    pages: 500,
    pricePerPage: this.price / this.pages
};

instead, you could do:

var book = {
    price: somePrice * discount,
    pages: 500
};
book.pricePerPage = book.price / book.pages;
// or book['pricePerPage'] = book.price / book.pages;

Dynamic property names:

If the property name is stored in some variable or created through some expression, then you have to use bracket notation:

var name = 'propertyName';

// the property will be `name`, not `propertyName`
var obj = {
    name: 42
}; 

// same here
obj.name = 42;

// this works, it will set `propertyName`
obj[name] = 42;

Solution 2:

There is various way to define a function. It is totally based upon your requirement. Below are the few styles :-

1. Object Constructor
2. Literal constructor
3. Function Based
4. Protoype Based
5. Function and Prototype Based
6. Singleton Based

Examples:

1. Object constructor

var person = new Object();

person.name = "Anand",
person.getName = function(){
  return this.name ; 
};

2. Literal constructor

var person = { 
  name : "Anand",
  getName : function (){
   return this.name
  } 
} 

3. function Constructor

function Person(name){
  this.name = name
  this.getName = function(){
    return this.name
  } 
} 

4. Prototype

function Person(){};

Person.prototype.name = "Anand";

5. Function/Prototype combination

function Person(name){
  this.name = name;
} 
Person.prototype.getName = function(){
  return this.name
} 

6. Singleton

var person = new function(){
  this.name = "Anand"
} 

You can try it on console, if you have any confusion.