Method add

src/core/data-structures/observable.js:22–30

* Adds the observer to this instance. * @param {function(TYPE=):void} handler Observer's handler. * @return {import('#core/types/function/types').UnlistenCallback}

(handler)

   * @return {import('#core/types/function/types').UnlistenCallback}
   */
  add(handler) {
    if (!this.handlers_) {
      this.handlers_ = [];
    }
    this.handlers_.push(handler);
    return () => {
      this.remove(handler);
    };
  }

  /**
   * Removes the observer from this instance.