Question

The following JavaScript code is very confusing to me. Could anyone help me understand. Why does PersonY not have prototype property.

PersonX = function(){};
PersonY = new function(){};
alert(PersonX.prototype);
alert(PersonY.prototype);    
​

Answer 1

PersonX = function(){};

Places a reference to an anonymous function into PersonX. PersonX points to a function.

PersonY = new function(){};

Places a reference to a newly constructed instance of an anonymous constructor function into PersonY. PersonY points to an object.

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Regarding the prototype, PersonY has one. However, since there were no properties and methods attached to the constructor before nor after instantiation, it has a blank prototype*.

You can actually check PersonY‘s prototype by doing console.log(PersonY). You will see that it has a prototype property (I see it as __proto__ in Chrome) which is “blank”. But it has 2 hidden properties, constructor which is the constructor function that made the object, and another __proto__ which leads you to the next “chain link” which would be the Object object.

_{*Not really blank since prototype is a chain. This prototype level may be blank, but the next higher prototype may have, or in this case, does have properties and methods.}

Object prototype -> Constructor prototype -> Your Instance will have:
- toString()        - blank                  - toString()
- hasOwnProperty()                           - hasOwnProperty()
- and more...                                - and more...
                                             - ...but nothing from Constructor