JavaScript super.constructor() throws "must call before accessing this" exception

Question

I'm trying to derive a class in JavaScript. Basically I have a class Auth (more like an interface) and a class UserLogin which extends from it. The problem is I get this exception even though I'm calling super.constructor() before anything else:

/Users/octav/Documents/work/framework-one/framework/server/src/user_login.js:12
        super.constructor(server);
        ^

ReferenceError: Must call super constructor in derived class before accessing 'this' or returning from derived constructor
    at new UserLogin (/Users/octav/Documents/work/framework-one/framework/server/src/user_login.js:12:3)
    at Object.<anonymous> (/Users/octav/Documents/work/framework-one/framework/server/app.js:8:14)
    at Module._compile (internal/modules/cjs/loader.js:955:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:991:10)
    at Module.load (internal/modules/cjs/loader.js:811:32)
    at Function.Module._load (internal/modules/cjs/loader.js:723:14)
    at Function.Module.runMain (internal/modules/cjs/loader.js:1043:10)
    at internal/main/run_main_module.js:17:11

The base class:

/*
 * Generic authentication class
 */

const ServerError = require("./server_error.js");

class Auth {

    constructor(server) {
        if (server === undefined || typeof("server") !== "object")
            throw new ServerError("Bad type or missing argument 'server'");
        this.server = server;
    }
...

The UserLogin class - as you can see I'm not calling this before calling the super constructor.

/*
 * User Login class
 */

const Auth = require("./auth.js");

const ServerError = require("./server_error.js");

class UserLogin extends Auth {

    constructor(server, config) {
        super.constructor(server); // <== This is where the error is triggered

        if (config === undefined || typeof(config) !== "object")
            throw new ServerError("Missing config or bad type");
        if (config.endpoints === undefined || typeof(config.endpoints) !== "object")
            throw new ServerError("Missing config.endpoints or bad type");
        if (config.endpoints.login === undefined || typeof(config.endpoints.login) !== "object")
            throw new ServerError("Missing config.endpoints.login or bad type");
        if (config.endpoints.logout === undefined || typeof(config.endpoints.logout) !== "object")
            throw new ServerError("Missing config.endpoints.logout or bad type");

        this.endpoints = config.endpoints;
    }
...

My start-up script:

const Server = require("./src/server.js");
const UserLogin = require("./src/user_login.js");

const config = require("./config.json");

const server = new Server(config);

const auth = new UserLogin(server, config.login); // <== This is where the error is triggered

server.setAuth(auth);

server.start();

I tried to look for answers online but all I could find were pages about how to derive classes in JavaScript.

Any ideas?

Answer 1

Inside the constructor of UserLogin class, you need to call super() first:

class UserLogin extends Auth {
    constructor(server, config) {
        super(); // you're missing this

        super.constructor(server);

        // ...
    }
}