unless x in y compiles to if (x in y)

      unless box in @all
        @boxes.push box
        @all.push box
        if @stopped or @disabled()
          @resetStyle()
        else
          @applyStyle(box, true)
        @scrolled = true

becomes

    for (let i = 0; i < iterable.length; i++) {
      let box = iterable[i];
      if (__in__(box, this.all)) {
        this.boxes.push(box);
        this.all.push(box);
        if (this.stopped || this.disabled()) {
          this.resetStyle();
        } else {
          this.applyStyle(box, true);
        }
        this.scrolled = true;
      }
    }

should be

    for (let i = 0; i < iterable.length; i++) {
      let box = iterable[i];
      if (!__in__(box, this.all)) {
        this.boxes.push(box);
        this.all.push(box);
        if (this.stopped || this.disabled()) {
          this.resetStyle();
        } else {
          this.applyStyle(box, true);
        }
        this.scrolled = true;
      }
    }

[eventualbuddha]

I believe all the examples raised on this issue are now fixed in v2.9.1.

[pvdz]

unless x instanceof y
  z

->

if (x instanceof y) {
  z;
}

😿