type Constructor<T> = new(...args: any[]) => T;

function mixin<T>(MixIn: Constructor<T>) {
    return function decorator<U>(Base: Constructor<U>) : Constructor<T & U> {
        Object.getOwnPropertyNames(MixIn.prototype).forEach(name => {
            Base.prototype[name] = MixIn.prototype[name];
        });

        return Base as Constructor<T & U>;
    }
}

class MixInClass {
    mixinMethod() {console.log('mixin method is called')}
}

/**
 *  apply mixin(MixInClass) implicitly (use decorator syntax)
 */
@mixin(MixInClass)
class Base1 {
    baseMethod1() { }
}
const m1 = new Base1();
m1.baseMethod1();
m1.mixinMethod(); // error TS2339: Property 'mixinMethod' does not exist on type 'Base1'.

/**
 *  apply mixin(MixInClass) explicitly
 */
class Base2 {
    baseMethod2() { }
}
const MixedBase2 = mixin(MixInClass)(Base2);
const m2 = new MixedBase2();
m2.baseMethod2();
m2.mixinMethod(); // OK

//...
var Base1 = /** @class */ (function () {
    function Base1() {
    }
    Base1.prototype.baseMethod1 = function () { };
    Base1 = __decorate([
        mixin(MixInClass)
    ], Base1);
    return Base1;
}());
//...