Crockford's Prototypical Inheritance - Usage

Question

I\'ve been building a small JS framework for use at my job, and I\'d like to employ Douglas Crockford\'s prototypical inheritance patterns. I think I get the general idea o

Answer 1

You got Object.create wrong. The first argument should be an object (maybe that's why people suggested you pass a literal).

In your first example, you're actually passing undefined:

Vehicles.Airplane = Object.create(Vehicles.Vehicle()); // the function call will
                                                       // return undefined

The following would work, but it's not very Crockford-ish:

Vehicles.Airplane = Object.create(new Vehicles.Vehicle());

The way I believe Crockford would do it (or, at least, wouldn't complain of):

var Vehicles = {};

Vehicles.Vehicle = {
    go : function() {
        // go stuff
    },
    stop : function() {
        // go stuff
    }
};

Vehicles.Airplane = Object.create(Vehicles.Vehicle, {
    takeOff : { 
        value : function() {
            // take-off stuff
        }
    },
    land : {
        value: function() {
            // land stuff
        }
    }
});

Note that Vehicles.Vehicle is just a literal, which will be used as the prototype for other objects. When we call Object.create, we pass Vehicles.Vehicle as the prototype, and takeOff and land will be own properties of Vehicles.Airplane. You may then call Object.create again, passing Vehicles.Airplane as the prototype, if you want to create e.g. a Boeing.

The own properties passed as the second parameter are packed in an object that contains a representation of their property descriptors. The outer keys are the names of your properties/methods, and each one points to another object containing the actual implementation as the value. You may also include other keys like enumerable; if you don't they'll take the default values. You can read more about descriptors on the MDN page about Object.defineProperty.