The thing is that I would like to use ES6 classes. There are some situations where it just feels so bad to do "if (this.doFoo !== undefined) { this.doFoo(); }"

The thing is that I would like to use ES6 classes. There are some situations where it just feels so bad to do "if (this.doFoo !== undefined) { this.doFoo(); }" because you can't really define empty interfaces in mixins. Subclassing would help a ton here.