CODEWITHSUNDEEP
javascriptinheritance
Brandon
Brandon

Reputation: 1195

Why isnt this simple inheritance working?

I'm trying to use the properties object parameter in Object.create, the mdn says you pass an object into it, but when I pass an object into it I get an error telling me to passing an object, I'm confused as to what I'm doing wrong

let mammal={hasFur:true}

let dog=Object.create(mammal,{legs:4});//returns Uncaught TypeError: Property description must be an object: true at Function.create (<anonymous>)

Upvotes: 1

Views: 114

Answers (2)

behkod
behkod

Reputation: 2777

In a simple definition, Object.create(proto[, propertiesObject]) is a mean for defining the abstract for object's properties, or defining specification of object's properties. It works like abstract classes in some of the other languages, & not a specific object.

It is not there to necessarily provide a default value for the props of the object being created. You have provided a literal (4) only, which is obviously not an object having the ability to describe specification for the property. We will see here, that 4 in its own is(even not necessarily) only a part of properties object for legs.

Now. with this in mind lets try to create your dog object using Object.create(). Here we go:

  • Requirements: we want our dog to have a property named legs.
  • design: we need legs to be enumerable while enumerating the object. we don't want to let others to change it with assignment operator. & also we want to default to 4.
  • Implementation: Now that we've decided on specification of legs property, we need a Property Descriptor to define it.[the second parameter of Object.defineProperties(obj, props)]

The props mentioned above is second{& optional} parameter in Object.create(proto[, propertiesObject]) & has some keys for describing properties of objects:

props {configurable, enumerable, value, writable, get, set}

Lets code the dog object:

let dog=Object.create(mammal,{
                      legs:{
                          enumerable : true,
                          writable : false,
                          value : 4 }
                     });

For more clarification, reading both of the references linked above, is highly helpful.

Upvotes: 2

Quentin
Quentin

Reputation: 943547

You've described legs as 4, and 4 is not an object.

See the MDN documentation which includes examples of the sorts of things you can assign there:

o = Object.create(Object.prototype, {
  // foo is a regular 'value property'
  foo: {
    writable: true,
    configurable: true,
    value: 'hello'
  },

In this example we use foo instead of legs. The value of an object, which includes a value property holding the default value for foo.

Upvotes: 3

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