Method _transitionTo

packages/zone.js/lib/zone-impl.ts:1462–1477

(toState: TaskState, fromState1: TaskState, fromState2?: TaskState)

    }

    _transitionTo(toState: TaskState, fromState1: TaskState, fromState2?: TaskState) {
      if (this._state === fromState1 || this._state === fromState2) {
        this._state = toState;
        if (toState == notScheduled) {
          this._zoneDelegates = null;
        }
      } else {
        throw new Error(
          `${this.type} '${
            this.source
          }': can not transition to '${toState}', expecting state '${fromState1}'${
            fromState2 ? " or '" + fromState2 + "'" : ''
          }, was '${this._state}'.`,
        );
      }
    }

    public toString() {
      if (this.data && typeof this.data.handleId !== 'undefined') {