3 ways to define a JavaScript class
Introduction
JavaScript is a very flexible object-oriented language when it comes to syntax. In this article you can find three ways of defining and instantiating an object. Even if you have already picked your favorite way of doing it, it helps to know some alternatives in order to read other people's code.It's important to note that there are no classes in JavaScript. Functions can be used to somewhat simulate classes, but in general JavaScript is a class-less language. Everything is an object. And when it comes to inheritance, objects inherit from objects, not classes from classes as in the "class"-ical languages.
1. Using a function
This is probably one of the most common ways. You define a normal JavaScript function and then create an object by using thenew keyword. To define properties and methods for an object created using function(), you use the this keyword, as seen in the following example.function Apple (type) { this.type = type; this.color = "red"; this.getInfo = getAppleInfo; } // anti-pattern! keep reading... function getAppleInfo() { return this.color + ' ' + this.type + ' apple'; }
var apple = new Apple('macintosh'); apple.color = "reddish"; alert(apple.getInfo());
1.1. Methods defined internally
In the example above you see that the method getInfo() of the Apple "class" was defined in a separate function getAppleInfo(). While this works fine, it has one drawback – you may end up defining a lot of these functions and they are all in the "global namespece". This means you may have naming conflicts if you (or another library you are using) decide to create another function with the same name. The way to prevent pollution of the global namespace, you can define your methods within the constructor function, like this:function Apple (type) { this.type = type; this.color = "red"; this.getInfo = function() { return this.color + ' ' + this.type + ' apple'; }; }
1.2. Methods added to the prototype
A drawback of 1.1. is that the method getInfo() is recreated every time you create a new object. Sometimes that may be what you want, but it's rare. A more inexpensive way is to add getInfo() to the prototype of the constructor function.function Apple (type) { this.type = type; this.color = "red"; } Apple.prototype.getInfo = function() { return this.color + ' ' + this.type + ' apple'; };
2. Using object literals
Literals are shorter way to define objects and arrays in JavaScript. To create an empty object using you can do:var o = {};instead of the "normal" way:
var o = new Object();For arrays you can do:
var a = [];instead of:
var a = new Array();So you can skip the class-like stuff and create an instance (object) immediately. Here's the same functionality as described in the previous examples, but using object literal syntax this time:
var apple = { type: "macintosh", color: "red", getInfo: function () { return this.color + ' ' + this.type + ' apple'; } }
apple.color = "reddish"; alert(apple.getInfo());
3. Singleton using a function
Again with the singleton, eh?
The third way presented in this article is a combination of the other two you already saw. You can use a function to define a singleton object. Here's the syntax:
var apple = new function() { this.type = "macintosh"; this.color = "red"; this.getInfo = function () { return this.color + ' ' + this.type + ' apple'; }; }
apple.color = "reddish"; alert(apple.getInfo());
new function(){...} does two things at the same time: define a function (an anonymous constructor function) and invoke it with new.
It might look a bit confusing if you're not used to it and it's not too
common, but hey, it's an option, when you really want a constructor
function that you'll use only once and there's no sense of giving it a
name.
In simple view we can insert, update, delete data. We can only insert data in simple view if we have primary key and all not null fields in the view.
We can only update data in complex view.We can't insert,update data in complex view.