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'.

[unional]

This is very problematic because it means my library (which rely on this) published in es5 cannot be consumed by JavaScript directly at all.

[mhegazy]

Automatically closing this issue for housekeeping purposes. The issue labels indicate that it is unactionable at the moment or has already been addressed.