Comment of Dean Edwards’s Base Library By John Resig

Download from "http://www.apress.com/book/downloadfile/3291"

// The Base object constructor
var Base = function(obj){
    // Only work if there's something to extend
    if (obj) 
        // If used as Base(), use the prototype of the caller
        if (this == window) 
            Base.prototype.extend.call(obj, arguments.callee.prototype);
        
        // Otherwise, this is called as new Base(), so extend the object
        else 
            this.extend(obj);
};

Base.version = "1.0.2";

Base.prototype = {
    // A function for overriding one object property with another
    extend: function(source, value){
        var extend = Base.prototype.extend;
        
        // Check to see if we're overriding a property with a new value
        if (arguments.length == 2) {
            // Remember the original parent property value
            var ancestor = this[source];
            
            // Check to see if we're overriding a parent method, and that this.base()
            // is actually used by the overrider
            if ((ancestor instanceof Function) && (value instanceof Function) &&
            ancestor.valueOf() != value.valueOf() &&
            /\bbase\b/.test(value)) {
            
                // Remember the old function
                var method = value;
                
                // and build a new function wrapper, to have sane 
                value = function(){
                    // Remember the old value of this.base to be restored later
                    var previous = this.base;
                    // Calling this.base() calls the old parent function
                    this.base = ancestor;
                    
                    // Execute the new, overriding, function
                    var returnValue = method.apply(this, arguments);
                    
                    // Restore the this.base() property
                    this.base = previous;
                    
                    // Return the accurate return value
                    return returnValue;
                };
                
                // valueOf and toString get messed by our modified
                // wrapper function, so make them appear normal
                value.valueOf = function(){
                    return method;
                };
                value.toString = function(){
                    return String(method);
                };
            }
            
            // Attach the new property to the source
            return this[source] = value;
            
            // If only a source was provided, copy all properties over from
            // the parent class to this new child
        }
        else 
            if (source) {
                var _prototype = {
                    toSource: null
                };
                
                // We modify these two functions later on, so protect them
                var _protected = ["toString", "valueOf"];
                
                // if we are prototyping then include the constructor
                if (Base._prototyping) 
                    _protected[2] = "constructor";
                
                // Copy over the protected functions indvidually
                for (var i = 0; (name = _protected[i]); i++) 
                    if (source[name] != _prototype[name]) 
                        extend.call(this, name, source[name]);
                
                // Copy each of the source object's properties to this object
                for (var name in source) 
                    if (!_prototype[name]) 
                        extend.call(this, name, source[name]);
            }
        
        return this;
    },
    
    // The this.base() function which we'll be implementating later on
    base: function(){
    }
};

// A wrapper function for creating a new object constructor
Base.extend = function(_instance, _static){
    // Remember the extend function
    var extend = Base.prototype.extend;
    
    // Lets us do Base.extend() and get a blank object constructor
    if (!_instance) 
        _instance = {};
    
    // Make sure to include the constructor later
    Base._prototyping = true;
    
    // Build the prototype
    var _prototype = new this;
    extend.call(_prototype, _instance);
    
    // Build the constructor
    var constructor = _prototype.constructor;
    _prototype.constructor = this;
    
    delete Base._prototyping;
    
    // Create the wrapper for the constructor function
    var klass = function(){
        if (!Base._prototyping) 
            constructor.apply(this, arguments);
        this.constructor = klass;
    };
    
    // Which inherits from Base
    klass.prototype = _prototype;
    
    // Add all the extra Base methods
    klass.extend = this.extend;
    klass.implement = this.implement;
    klass.toString = function(){
        return String(constructor);
    };
    
    // Add in all the extra properties provided by the user
    extend.call(klass, _static);
    
    // Check for a single instance case
    var object = constructor ? klass : _prototype;
    
    // Class initialisation
    if (object.init instanceof Function) 
        object.init();
    
    // Return the new object constructor
    return object;
};

// A simple function that can be used to pull additional object properties
// into a constructor – effectively creating multiple inheritance
Base.implement = function(_interface){
    // If a constructor was provided, instead of a prototype,
    // get the prototype instead
    if (_interface instanceof Function) 
        _interface = _interface.prototype;
    
    // Extend the object with the methods from the parent object
    this.prototype.extend(_interface);
};