Object being recognized as null or undefined

Question

I'm trying to assign housePrototype as the prototype of House object, and followed up with this error

Object.assign(House.prototype, this.housePrototype); ^ TypeError: Cannot convert undefined or null to object

What am I doing wrong?

const House = {
    name: 'houseObject',
     readLocation: (location)=>{
      console.log(`house is located at ${location}`)
    }
  }

  const housePrototype = {
    readLocation: (location) => {
    console.log(`house prototype is located at ${location}`)
    }
  }

  Object.assign(House.prototype, housePrototype)
  
  House.readLocation('Malabe');
  console.log(House);

But https://developer.mozilla.org/en-US/docs/Learn/JavaScript/Objects/Object_prototypes article saying we can set prototype in assign method as below. Can you explain please? — Inod Umayanga, Sep 09 '22 at 03:16
you've read that page wrong ... notice the code where `Object.assign(Person.prototype, personPrototype);` is used ... check what `Person` is and compare it to what `House` is — Jaromanda X, Sep 09 '22 at 03:19
@JaromandaX Person is a function and House is an abject but aren't they both supposed to have prototypes? Functions are also objects in JavaScript right? — Inod Umayanga, Sep 09 '22 at 03:25
@TimoDevs console.log(House.__proto__) prints its prototype to the console doesn't the House.prototype does the same for regular objects? (not function objects) — Inod Umayanga, Sep 09 '22 at 03:29
`console.log({}.prototype)` vs `console.log(function() {}.prototype)` should answer your question — Jaromanda X, Sep 09 '22 at 03:29
@JaromandaX oh wow never realized the difference till now thank you so much — Inod Umayanga, Sep 09 '22 at 03:39
@InodUmayanga Both objects have prototypes: `Object.getPrototypeOf(House)`, `Object.getPrototypeOf(Person)`. But only the constructor function has a `.prototype` property. — Bergi, Sep 09 '22 at 12:37

Inod Umayanga · Accepted Answer · 2022-09-10T06:43:52.583

All credit goes to @JaromandaX. He explained the issue in the comments of the question.

Even though functions are Objects in JavaScript they are NOT identical. To access the prototype of a function function() {}.prototype can be used. But in the question, it is trying to access the prototype of a regular object, not a function object, which is undefined, thus the error.

Object.assign(House.__proto__, housePrototype);

With this it is possible to assign desired object to the prototype (It is not recommended to assign any variables to proto and it si not at all a common pra)

The solution code would be

const House = {
    name: 'houseObject',
     readLocation: (location)=>{
      console.log(`house is located at ${location}`)
    }
  }

  const housePrototype = {
    readLocation: (location) => {
    console.log(`house prototype is located at ${location}`)
    }
  }

  Object.assign(House.__proto__, housePrototype)
  
  House.readLocation('Malabe');

I found a complete description in following StackOverflow thread __proto__ VS. prototype in JavaScript

No, don't do that. `House.__proto__` is `Object.prototype`, and you should absolutely not assign any properties to that. — Bergi, Sep 09 '22 at 12:38
@Bergi Thanks and I will not use __proto__ anywhere in a production code. I'll edit the answer not recommending to use it further — Inod Umayanga, Sep 10 '22 at 06:40

score -2 · Answer 2 · answered Sep 09 '22 at 03:13

Hey Bro the problem is House.prototpe because the object house has no object called prototype there are only two name and readLocation so change code to this : from this :

const House = {
    name: 'houseObject',
     readLocation: (location)=>{
      console.log(`house is located at ${location}`)
    }
  }

  const housePrototype = {
    readLocation: (location) => {
    console.log(`house prototype is located at ${location}`)
    }
  }

  Object.assign(House.prototype, housePrototype)
  
  House.readLocation('Malabe');
  console.log(House);

to this :

const House = {
    name: 'houseObject',
     readLocation: (location)=>{
      console.log(`house is located at ${location}`)
    }
  }

  const housePrototype = {
    readLocation: (location) => {
    console.log(`house prototype is located at ${location}`)
    }
  }

  Object.assign(House, housePrototype)
  
  House.readLocation('Malabe');
  console.log(House);

As it’s currently written, your answer is unclear. Please [edit] to add additional details that will help others understand how this addresses the question asked. You can find more information on how to write good answers [in the help center](/help/how-to-answer). — Community, Sep 14 '22 at 01:17

score -2 · Answer 3 · answered Sep 09 '22 at 03:15

-2

Usefull docs: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/assign#try_it

const House = {
  name: 'houseObject',
  readLocation: (location)=>{
    console.log(`house is located at ${location}`)
  }
}

const housePrototype = {
  readLocation: (location) => {
    console.log(`house prototype is located at ${location}`)
  }
}

//Object.assign(target, src);
Object.assign(House, housePrototype);

House.readLocation('Malabe');
console.log(House);

answered Sep 09 '22 at 03:15

Daniel Madrid

1

As it’s currently written, your answer is unclear. Please [edit] to add additional details that will help others understand how this addresses the question asked. You can find more information on how to write good answers [in the help center](/help/how-to-answer). – Community Sep 13 '22 at 23:32

Object being recognized as null or undefined

3 Answers3