A JavaScript inheritance model

inheritance.js

(function() {
    // Parent Class
    this.ClassA = function() {

        var defaults = {
            setting1: null,
            setting2: 'hello',
        }

        // Create options by extending defaults with the passed in arugments
        if (typeof arguments[0] === "object") {
            this.options = this.extend(defaults, arguments[0]);
        }
    }
    // This is a utility method for extending an options object
    ClassA.prototype.extend = function(source, properties){
        var property;
        for (property in properties) {
            if (properties.hasOwnProperty(property)) {
                source[property] = properties[property];
            }
        }
        return source;
    }
    // This is a utility method for merging 3 option sets into one
    ClassA.prototype.mergeOptions = function(global,defaults,local){
        var options = {};
        // Merge global options with defaults. Defaults wins
        if (typeof global === "object") {
            options = this.extend(defaults, global);
        }
        // Merge options with local. Local wins
        if (typeof local === "object") {
            options = this.extend(options,local);
        }
        return options;
    }
    // Test Log method
    ClassA.prototype.log = function(){
        console.log('This is Class A');
    }

}());

(function() {
    // Child Class
    this.ClassB = function() {

        // Inheritance to Class A
        ClassA.call(this);

        // Define option defaults
        var defaults = {
            setting1: 'yo yo',
            setting2: true,
        }

        // this.options is populated from ClassA.call()
        // merge those with defaults and arguments passed
        this.options = ClassA.prototype.mergeOptions(this.options,defaults,arguments[0]);
    }
    // Inheritance to Class A - this gets all prototypes
    ClassB.prototype = Object.create(ClassA.prototype);

    ClassB.prototype.log = function(){
        console.log('This is Class B');
    }

}());

//-----------------------------------------------
// Implementation
//-----------------------------------------------
var b = new ClassB({'setting1':'Caio'});
b.log();