How can I create a subtype of Error to throw it?

Question

I am trying to throw my own kind of error, so that when catching I can call if(instanceof DatabaseError) and handle it my own way.

export class DatabaseError extends Error {
    constructor(...args: string[] | undefined[]) {
        super(...args);
        this.name = "DatabaseError"
    }
}

const err: DatabaseError = new DatabaseError(`Message`);
console.log(Object.getPrototypeOf(err));

However, it looks like for all intents and purposes, err is not an instance of DatabaseError. The log returns Error {} , and instanceof DatabaseError returns false. What have I done wrong, and what is the correct way to introduce new Errors so that I can handle them differenty? Or should I create an object that doesn't inherit from Error?

Here is the tsconfig.json I am using:

{
  "compilerOptions": {
    "target": "es6", /* Specify ECMAScript target version: 'ES3' (default), 'ES5', 'ES2015', 'ES2016', 'ES2017', 'ES2018', 'ES2019', 'ES2020', or 'ESNEXT'. */
    "module": "commonjs", /* Specify module code generation: 'none', 'commonjs', 'amd', 'system', 'umd', 'es2015', 'es2020', or 'ESNext'. */
    /* Strict Type-Checking Options */
    "strict": true, /* Enable all strict type-checking options. */
    "esModuleInterop": true, /* Enables emit interoperability between CommonJS and ES Modules via creation of namespace objects for all imports. Implies 'allowSyntheticDefaultImports'. */
    /* Advanced Options */
    "skipLibCheck": true, /* Skip type checking of declaration files. */
    "forceConsistentCasingInFileNames": true /* Disallow inconsistently-cased references to the same file. */
  }
}

Answer 1

Are You sure you tried instanceof ?

export class DatabaseError extends Error {
    constructor(...args: string[] | undefined[]) {
        super(...args);
        this.name = "DatabaseError"
    }
}

const err: DatabaseError = new DatabaseError(`Message`);
err instanceof DatabaseError // true

You can try this conde in your console, just don't forget remove type anotations. It works for me as expected.

You don't need to use getPrototypeOf