text: class SerialLoadHistory extends ClsObject {
      #_PV = {};
  
      // ctor
      constructor(name) {
          super(name);
  
          try {
              this.#_PV.history = new Map();
          } catch (e) {
              var m = this.getExpMsg("ctor", e);
              console.log(m);
              alert(m);
          }
      }
  
      // reserved asset key
      set ReservedKey(key) {
          this.#_PV.assetKey = key;
      }
  
      // add complete asset key
      addReservedKey() {
          try {
              if (this.#_PV.assetKey == undefined) {
                  //console.log("no reserved-key");
                  return; 
              }
  
              this.#_PV.history.set(this.#_PV.assetKey, true);
              this.#_PV.assetKey = undefined;
          } catch (e) {
              var m = this.getExpMsg("addReservedKey", e);
              console.log(m);
              alert(m);
          }
      }
  
      // 로딩 확인
      isLoadedAsset(key) {
          try {
              return this.#_PV.history.has(key);
          } catch (e) {
              var m = this.getExpMsg("isLoadedAsset", e);
              console.log(m);
              alert(m);
          }
      }
  }