Add Function to JavaScript Object using Object.Create

Question

I'm trying to use Object.Create in JavaScript. I currently have the following code:

var vehicle = {
        getModel: function () {
        console.log( "The model of this vehicle is.." + this.model );
    }
};

var car = Object.create(vehicle, {
    "id": {
       value: 9,         
    },
    "model": {
       value: "Ford",  
    }
});

var van = Object.create(vehicle, {
  "id": {
     value: 10,    
   },
    "model": {
      value: "Big Van",
      enumerable: true
   },
    "make": {
      value: "Warrior",      
   },
    "getMake": function () {
       console.log( "The make of this vehicle is.." + this.make );
   }
});

I've tried to add a function to van for getMake but I get the error:

TypeError: Property 'getMake' of object # is not a function when I call:

van.getMake();

Is this possible? How do you do it?

Not only have I never used it, but I didn't know it even existed... — David Thomas
– David Thomas, Commented Nov 26, 2012 at 13:05

Ryan O'Neill · Accepted Answer · 2012-11-26 13:10:46Z

6

Properties created that way are not enumerable by default. This may be causing your issue.

Try this(untested):

"getMake": { value: function () {
       console.log( "The make of this vehicle is.." + this.make )
   }, enumerable: true };

Edit It looks like this is working because we are passing an object and not just the value. The enumerable is unnecessary.

edited Nov 26, 2012 at 13:10

answered Nov 26, 2012 at 13:01

Ryan O'Neill

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3 Comments

Denys Séguret Over a year ago

No need for the property to be enumerable.

Elias Van Ootegem Over a year ago

I'm with @dystroy, I'd even argue that the property is best defined as enumerable: false, when iterating an object (for (var p in obj)), you generally don't want to deal with the methods

Mahendra Singh Over a year ago

But the default behaviour is to list all enumerable properties, and methods are enumerable by default.So its good to go with the enumerable:true as it is more towards the expected default behaviour.

Denys Séguret · Accepted Answer · 2012-11-26 13:03:17Z

2

You need to pass an object defining the property, not just the value :

 "getMake": {value:function () {
     console.log( "The make of this vehicle is.." + this.make );
 }}

Reference

Note that the usual way to do OOP in Javascript isn't in using Object.create but in using prototype.

answered Nov 26, 2012 at 13:03

Denys Séguret

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1 Comment

Denys Séguret Over a year ago

In my own opinion it's ugly, useless and slow. But, as most js coders I never use Object.create so I may miss some of its advantages.

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