问流行的JavaScript继承模式

EN

// Pseudoclassical Inheritance
    function Animal(name) {
        this.name = name;
        this.arr = [1,2,3];
    };
    Animal.prototype = {
        constructor: Animal,
        whoAmI: function() { return "I am " + this.name + "!\n"; }
    };

    function Dog(name, breed) {
        this.name = name;
        this.breed = breed;
    };
    Dog.prototype = new Animal();
    Dog.prototype.getBreed = function() {
        return this.breed;
    };
    Dog.prototype.bark = function() {
        return 'ruff ruff';
    };

    // Combination Inheritance
    function Parent(name) {
        this.name = name;
        this.arr = [1,2,3];
    };
    Parent.prototype = {
        constructor: Parent,
        toString: function() { return "My name is " + this.name; }
    };
    function Child(name, age) {
        Parent.call(this, name);
        this.age = age;
    };

    Child.prototype = new Parent();

    Child.prototype.getAge = function() {
        return this.age;
    };

    // Prototypal Inheritance
    var helper = { // Thanks to Bob Vince for reminding me NOT to clobber Object!

        inherit: function(p) {
        NewObj = function(){};
        NewObj.prototype = p;
        return new NewObj(); 
        },
        inheritPrototype: function(subType, superType) {
        var prototype = helper.inherit(superType.prototype);
        prototype.constructor = subType;
        subType.prototype = prototype;
        }
    };

    function SubType(name, age) {
        Parent.call(this, name);
        this.age = age;    
    };
    //Child.prototype = new Parent();   // Gets replaced by:
    helper.inheritPrototype(SubType, Parent);  
    SubType.prototype.getAge = function() {
        return this.age;
    };

    // Functional - Durable Pattern
    function super_func(blueprint) { 
        var obj = {};
        obj.getName = function() { return blueprint.name; };
        obj.getAge  = function() { return blueprint.age; };
        obj.getFoo  = function() { return blueprint.foo; };
        obj.getBar  = function() { return blueprint.bar; };
        return obj;
    };
    function sub_func(blueprint) {
        blueprint.name = blueprint.name || "Crockford's Place";
        supr = super_func(blueprint);
        supr.coolAugment = function() { return "I give a fresh new perspective on things!" };
        return supr;    
    };

describe 'JavaScript Inheritance Tests'
    before_each
    animal = new Animal("Onyx")
    dog = new Dog("Sebastian", "Lab")

    person = { password : 'secret', toString : function(){ return '<Person>' } }
    stub(person, 'toString').and_return('Original toString method!')    
    end
    describe 'Pseudoclassical Inheritance Creation'
    it 'should create parent and child object using pseudoclassical inheritance'
        animal.constructor.should.eql Animal
        // dog.constructor.should.eql Dog // Nope: expected Animal to eql Dog
        dog.constructor.should.eql Animal 
        animal.should.be_a Animal 
        dog.should.be_a Animal
        // dog.should.be_a Dog // Nope! We severed the original prototype pointer and now point to Animal!
        dog.should.be_an_instance_of Animal
        dog.should.be_an_instance_of Dog 
        (animal instanceof Dog).should.be_false
    end
    it 'should behave such that child inherits methods and instance variables defined in parent'
        animal.whoAmI().should.match /I am Onyx.*/ 
        dog.whoAmI().should.match /Sebastian.*/
        animal.should.respond_to 'whoAmI'
        dog.should.respond_to 'whoAmI'
        dog.should.have_prop 'name'
    end
    it 'should behave such that methods and instance variables added to child are NOT available to parent'
        dog.bark().should.match /Ruff Ruff/i
        dog.should.have_property 'breed'
        dog.should.respond_to 'bark'
        // animal.should.have_prop 'breed' // Of course not!
        // animal.should.respond_to 'bark' // Of course not!
    end
    it 'should behave such that reference variables on the parent are "staticy" to all child instances'
        dog.arr.should.eql([1,2,3]) 
        dog.arr.push(4)
        dog.arr.should.eql([1,2,3,4]) 
        spike = new Dog("Spike", "Pitbull")
        spike.arr.should.eql([1,2,3,4]) 
        spike.arr.push(5)
        rover = new Dog("Rover", "German Sheppard")
        spike.arr.should.eql([1,2,3,4,5])
        rover.arr.should.eql([1,2,3,4,5])
        dog.arr.should.eql([1,2,3,4,5])
    end 
    end

    describe 'Combination Inheritance Solves Static Prototype Properties Issue'
    it 'should maintain separate state for each child object'
        child_1 = new Child("David", 21)
        child_2 = new Child("Peter", 32)
        child_1.arr.push(999)
        child_2.arr.push(333)
        child_1.arr.should.eql([1,2,3,999])
        child_2.arr.should.eql([1,2,3,333])
        child_1.getAge().should.eql 21
        child_1.should.be_a Parent
    end
    end

    describe 'Prototypal Inheritance'
    it 'should inherit properties from parent'
        person.toString().should.match /Original toString.*/i
        person.password.should.eql 'secret'
        joe = helper.inherit(person)
        joe.password.should.eql 'secret'
        joe.password = 'letmein'
        joe.password.should.eql 'letmein'
        person.password.should.eql 'secret'
    end
    end

    describe 'Parisitic Combination Inheritance'
    it 'should use inheritPrototype (to call parent constructor once) and still work as expected'
        sub = new SubType("Nicholas Zakas", 29)
        sub.toString().should.match /.*Nicholas Zakas/
        sub.getAge().should.eql 29
        charlie = new SubType("Charlie Brown", 69)
        charlie.arr.should.eql([1,2,3])
        charlie.arr.push(999)
        charlie.arr.should.eql([1,2,3,999])
        sub.arr.should.eql([1,2,3]) 
        sub.should.be_an_instance_of SubType
        charlie.should.be_an_instance_of SubType
        (sub instanceof SubType).should.eql true 
        (sub instanceof Parent).should.eql true 
    end
    end

    describe 'Functional Durable Inheritance'
    it 'should hide private variables'
        sup = new super_func( {name: "Superfly Douglas", age: 39, foo: "foo", bar: "bar"} )
        sup.getName().should.eql 'Superfly Douglas'
        sup.name.should.be_undefined
        sup.getAge().should.eql 39 
        sup.age.should.be_undefined
        sup.getFoo().should.eql 'foo'
        sup.foo.should.be_undefined
    end

    it 'should create a descendent object that inherits properties while maintaining privacy'
        sub = new sub_func( {name: "Submarine", age: 1, foo: "food", bar: "barfly"} )
        sub.getName().should.eql 'Submarine'
        sub.name.should.be_undefined
        sub.getAge().should.eql 1 
        sub.age.should.be_undefined
        sub.getFoo().should.eql 'food'
        sub.foo.should.be_undefined 
        sub.getBar().should.eql 'barfly'
        sub.bar.should.be_undefined 
        sub.coolAugment().should.match /.*fresh new perspective.*/
        //sub.should.be_an_instance_of super_func NOPE!
        //sub.should.be_an_instance_of sub_func   NOPE!
        sub.should.be_an_instance_of Object 
    end
    end

end