"Class extends value #

Question

Thanks for reading my post I get this error on my code : "Class extends value # is not a constructor or null" Here is my code, I'm trying to export/import classes.

monster.js :

const miniMonster = require("./minimonster.js");

class monster {
  constructor(options = { name }, health) {
    this.options = options;
    this.health = 100;
    this.heal = () => {
      return (this.health += 10);
    };
  }
}

let bigMonster = new monster("Godzilla");
console.log(bigMonster);

console.log(bigMonster.heal());

let mini = new miniMonster("Demon");
console.log(mini);
console.log(mini.heal());

module.exports = monster;

minimonster.js :

const monster = require("./monster.js");

class miniMonster extends monster {
  constructor(options) {
    super(options);
    this.health = 50;
    this.heal = () => {
      return (this.health += 5);
    };
  }
}

let miniM = new miniMonster("Jon");
console.log(miniM);

module.exports = miniMonster;

Thank you for any help given,

Have a good day

I would suggest to refactor your code to get rid of circular dependencies because it can get messy. You might add a third class that would manage those two. — Matus Dubrava, Apr 16 '18 at 10:24
aren't these 2 files including each other and depending on that? One class is probably not defined at one point — Kaddath, Apr 16 '18 at 10:24

score 23 · Accepted Answer · answered Apr 16 '18 at 10:23

I see at least one issue with your requires.

monster.js first line is const miniMonster = require("./minimonster.js");
minimonster.js first line is const monster = require("./monster.js");

This is a problem, you can not have both files evaluate at the same time. I would not require minimonster from monster.js

This may fix your issue.

score 18 · Answer 2 · answered Sep 19 '19 at 22:20

18

When I get this error message it is because I have done my module.exports wrong. eg.

publicclass.js

class PublicClass {
.....
}

module.exports.PublicClass = PublicClass;

instead of

module.exports = PublicClass;

answered Sep 19 '19 at 22:20

Dave Pile

5,559
3
34
49

1

Didn't even think about looking at the exports. This fixed it for me. Thanks! – Sv443 Sep 23 '19 at 09:38
I owe you a beer buddy – sebastianf182 Apr 14 '22 at 16:30
I put extended class in {} (within child class): `const { ParentClass} = require("./ParentClass");` – ParisaN Nov 18 '22 at 20:19

score 6 · Answer 3 · answered Dec 11 '19 at 01:26

6

For me, I had introduced a circular dependency.

answered Dec 11 '19 at 01:26

lwdthe1

1,001
1
16
16

score 1 · Answer 4 · answered May 22 '21 at 08:53

Correct Code:

//Export from monster.js (but don't import minimonster.js)
class monster {
.....
}
let bigMonster = new monster("Godzilla");
module.exports = monster;

//Import in minimonster.js
const monster = require("./monster.js");
class miniMonster extends monster {
.....
}
let miniM = new miniMonster("Jon");
module.exports = miniMonster;

A circular dependency happens when module A depends on something in module B and module B depends on something in module A. This means to compile module A you must first compile module B, but you can't do that as B requires A to be already compiled.

So to avoid circular dependency we should not import a module (minimonster.js) that is exporting a module (monster.js) in that same module (monster.js).

score 0 · Answer 5 · answered Nov 18 '22 at 20:22

In my case, I put extended class inside of {}.

const { ParentClass } = require("./ParentClass");

class ChildClass extends ParentClass {    
}

module.exports = { ChildClass };

And:

class ParentClass {
    constructor() {}
}

module.exports = { ParentClass };

score -7 · Answer 6 · edited Dec 02 '19 at 07:18

-7

I used as per below line.

import Base from "./base

and its working fine now

edited Dec 02 '19 at 07:18

Avinash Dalvi

8,551
7
27
53

answered Dec 02 '19 at 06:49

Rahul Mogar

1

6 Answers6