mixes.js

let behaviorA = {
  greet(greeting) {
    return greeting;
  }
};


@mixes(behaviorA)
class Foo {
  test() {
    return this.greet('hi from Foo');
  }
}

console.log( new Foo().test() );


// mix behaviors into a class.
function mixes(...behaviors) {
  return target => behaviors.forEach( b => Object.assign(target.prototype, b));
}