Mixin

Here is a good solution : https://github.com/Microsoft/TypeScript/issues/6502#issuecomment-173312747 that uses `Object.assign`

https://github.com/Microsoft/TypeScript/issues/2919#issuecomment-173384825

``` ts
function Mixin(...mixins) : new() => T {
class X {
constructor() {
mixins[0].call(this);
}
}
Object.assign(X.prototype, ...mixins.map(m => m.prototype));
return X;
}

abstract class Dog {
bark() { console.log('bark!'); }
}

abstract class Duck {
quack() { console.log('quack!'); }
}

class Base {
constructor() {
console.log('base ctor');
}

world = "world";

hello() {
console.log(`hello ${this.world}`);
}
}

interface DoggyDuck extends Base, Dog, Duck { }

class Mutant extends Mixin(Base, Dog, Duck) {

}

let xavier = new Mutant();
xavier.bark();
xavier.quack();
xavier.hello();
```

Start with the two linked TypeScript discussions and compare their Object.assign mixin approach with the TypeScript book’s existing coverage. Done means documenting a verified Mixin pattern based on the shown example, including its constructor and inherited methods.

Written by the indexing model from the issue text.