OOP in Javascript (with Node) | Chinese Rule of Eight

ref – http://book.mixu.net/node/ch6.html

The new constructor call (e.g. new Foo()):
creates a new object,
sets the prototype of that object to Foo.prototype and
passes that as this to the constructor.

The prototype chain lookup mechanism is the essence of prototypal inheritance.

// Constructor

function Foo(bar) {

// always initialize all instance properties

this.bar = bar;

this.baz = 'baz'; // default value

}

// class methods

Foo.prototype.fooBar = function() {

};

// export the class

module.exports = Foo;

Instantiate the class:

1 2	// constructor call var object = new Foo('Hello');

Adding private variables

// Private variable

var total = 0;

// Constructor

function Foo() {

// access private shared variable

total++;

};

// Expose a getter (could also expose a setter to make it a public variable)

Foo.prototype.getTotalObjects = function(){

return total;

};

Avoid assigning variables to prototypes

If you want to define a default value for a property of an instance, define it in the constructor function.

Prototypes should not have properties that are not functions, because prototype properties that are not primitives (such as arrays and objects) will not behave as one would expect, since they will use the instance that is looked up from the prototype. Example for Dimitry Sosnikov’s site:

var Foo = function (name) { this.name = name; };

Foo.prototype.data = [1, 2, 3]; // setting a non-primitive property

Foo.prototype.showData = function () { console.log(this.name, this.data); };

var foo1 = new Foo("foo1");

var foo2 = new Foo("foo2");

// both instances use the same default value of data

foo1.showData(); // "foo1", [1, 2, 3]

foo2.showData(); // "foo2", [1, 2, 3]

// however, if we change the data from one instance

foo1.data.push(4);

// it mirrors on the second instance

foo1.showData(); // "foo1", [1, 2, 3, 4]

foo2.showData(); // "foo2", [1, 2, 3, 4]

Hence prototypes should only define methods, not data.

function Foo(name) {

this.name = name;

this.data = [1, 2, 3]; // setting a non-primitive property

};

Foo.prototype.showData = function () { console.log(this.name, this.data); };

var foo1 = new Foo("foo1");

var foo2 = new Foo("foo2");

foo1.data.push(4);

foo1.showData(); // "foo1", [1, 2, 3, 4]