There's no syntactic support for class-based inheritance, so it's a bit verbose, but not really complicated:
function AClass(foo) {
this.foo = foo;
}
// methods are shared between instances
AClass.prototype.alertFoo = function() {
alert(this.foo);
};
function ASubClass(foo, bar) {
// call parent constructor
AClass.call(this, foo);
this.bar = bar;
}
// simulate inheritance via method aggregation
for(var name in AClass.prototype) {
if(AClass.prototype.hasOwnProperty(name))
ASubClass.prototype[name] = AClass.prototype[name];
}
// alternatively, use proper inheritance
ASubClass.prototype = Object.create(AClass.prototype);
ASubClass.prototype.alertFooBar = function() {
alert(this.foo + ' ' + this.bar);
};
Instead of adding methods to the prototype, you can also add them to the instance within the constructor. This way, you can simulate private members as such methods close over the constructor's lexical scope -- but this comes with a performance penalty.
Most custom class implementations just provide sugar over these patterns.
The following example illustrate how one may have private and public members as well as private and public methods and how to access them.
function AClass(foo)
{
this.foo = foo; // public member variable
var bar = "bar"; // private member variable
function fun1() // private method
{
bar = this.foo; // private and public var access
}
this.fun2 = function () // public privileged method
{
bar = this.foo; // private and public var access
}
}
This is all very different from other OOP languages. I just add these for clarification. It may be helpful to some readers.
By convention one may also add an underscore in front of private members and function identifiers to make the difference clearly visible in the code.
Would Object.create also inherit private functions and members ?
No, it would not - these so-called private members and methods have nothing to do with inheritance, but rather lexical closure.
However, as the super constructor is called, priviledged methods will be present and still have access to the private variables.
See also http://stackoverflow.com/a/1441692/48015 for a more comprehensive overview over different access levels.
The missing infos in the StackOverflow answer are how do one instantiate such class and access it's methods and public and shared members ? var obj = new MyObj() ? obj.publicSharedVar ?