Mixed es5/es2015 code with mixin classes causes runtime errors

TypeScript Version: 2.4.1 (but likely anything since 2.2)

When utilising code targeted at ES5 mixed with code targeted at ES6 causes a runtime error when using mixin classes. The real world use case was using a library that was targeted at ES5 for distribution compatibility reasons while downstream code is being targeted at ES2017 because of running in a known limited environment.

Code

Tagged.ts

// @target: es5
export interface Constructor<T> {
    new(...args: any[]): T;
    prototype: T;
}

export default function Tagged<T extends Constructor<{}>>(Base: T) {
    return class extends Base {
        _tag = '';
    }
}

TaggedExample.ts

// @target: es2015
import Tagged from './Tagged';

class Example {
  log() {
    console.log('Hello World!');
  }
}

const TaggedExample = Tagged(Example);

const taggedExample = new TaggedExample(); // Uncaught TypeError: Class constructor Example cannot be invoked without 'new'

Expected behavior:

No run-time errors.

Actual behavior:

A runtime error of Uncaught TypeError: Class constructor Example cannot be invoked without 'new'.

Inizia con gli snippet Tagged.ts e TaggedExample.ts e compilali usando i target ES5 ed ES2015 indicati per ispezionare il JavaScript generato. Traccia il modo in cui l’output del mixin ES5 invoca la classe base ES2015, quindi aggiungi una copertura di regressione che dimostri che l’esempio con target misti viene eseguito senza errori a runtime.