How to use the @angular/animations.AnimationMetadataType.State function in @angular/animations

metadata.definitions.forEach(def => {
      this._resetContextStyleTimingState(context);
      if (def.type == AnimationMetadataType.State) {
        const stateDef = def as AnimationStateMetadata;
        const name = stateDef.name;
        name.split(/\s*,\s*/).forEach(n => {
          stateDef.name = n;
          states.push(this.visitState(stateDef, context));
        });
        stateDef.name = name;
      } else if (def.type == AnimationMetadataType.Transition) {
        const transition = this.visitTransition(def as AnimationTransitionMetadata, context);
        queryCount += transition.queryCount;
        depCount += transition.depCount;
        transitions.push(transition);
      } else {
        context.errors.push(
            'only state() and transition() definitions can sit inside of a trigger()');
      }