Method getState

packages/designer/src/document/history.ts:170–186

* | 1 | 1 | 1 | * | -------- | -------- | -------- | * | modified | redoable | undoable |

()

   *  | modified | redoable | undoable |
   */
  getState(): number {
    const { cursor } = this.session;
    let state = 7;
    // undoable ?
    if (cursor <= 0) {
      state -= 1;
    }
    // redoable ?
    if (cursor >= this.records.length - 1) {
      state -= 2;
    }
    // modified ?
    if (this.point === cursor) {
      state -= 4;
    }
    return state;
  }

  /**
   * 监听 state 变更事件