Method setObservation_

src/utils/display-observer.js:378–397

* @param {!Element} target * @param {number} index * @param {?boolean} value * @param {?Array<!ObserverCallbackDef>} callbacks * @private

(target, index, value, callbacks)

   * @private
   */
  setObservation_(target, index, value, callbacks) {
    let observations = this.targetObservations_.get(target);
    if (!observations) {
      const observers = this.observers_;
      observations = new Array(observers.length);
      for (let i = 0; i < observers.length; i++) {
        observations[i] = observers[i].io ? null : false;
      }
      this.targetObservations_.set(target, observations);
    }

    if (callbacks) {
      const oldDisplay = computeDisplay(observations, this.isDocDisplay_);
      observations[index] = value;
      const newDisplay = computeDisplay(observations, this.isDocDisplay_);
      notifyIfChanged(callbacks, target, newDisplay, oldDisplay);
    } else {
      observations[index] = value;
    }
  }
}

/**