javascript

Chapter 6: Object-Oriented Programming
resolves to person.name . Early JavaScript developers used this pattern frequently to create new objects.
There was an obvious downside to this approach: creating multiple objects with the same interface
requires a lot of code duplication. To solve this problem, developers began using a variation of the
factory pattern.
The Factory Pattern
The factory pattern is a well - known design pattern used in software engineering to abstract away the
process of creating specific objects (other design patterns and their implementation in JavaScript are
discussed later in the book). With no way to define classes in ECMAScript, developers created functions
to encapsulate the creation of objects with specific interfaces, such as in this example:
function createPerson(name, age, job){
var o = new Object();
o.name = name;
o.age = age;
o.job = job;
o.sayName = function(){
alert(this.name);
};
return o;
}
var person1 = createPerson(“Nicholas”, 29, “Software Engineer”);
var person2 = createPerson(“Greg”, 27, “Doctor”);
Here, the function createPerson() accepts arguments with which to build an object with all of the
necessary information to represent a Person object. The function can be called any number of times with
different arguments and will still return an object that has three properties and one method. Though this
solved the problem of creating multiple similar objects, the factory pattern didn ’ t address the issue of object
identification (what type of object an object is). As JavaScript continued to evolve, a new pattern emerged.
The Constructor Pattern
As mentioned in previous chapters, constructors in ECMAScript are used to create specific types of
objects. There are native constructors, such as Object and Array , which are available automatically in
the execution environment at runtime. It is also possible to define custom constructors that define
properties and methods for your own type of object. For instance, the previous example can be rewritten
using the constructor pattern as the following:
function Person(name, age, job){
this.name = name;
this.age = age;
this.job = job;
this.sayName = function(){
alert(this.name);
};
}
var person1 = new Person(“Nicholas”, 29, “Software Engineer”);
var person2 = new Person(“Greg”, 27, “Doctor”);
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