Method updateNavigationButtons

js/ReadingSystem.js:705–714

* 更新导航按钮状态

()

   * 更新导航按钮状态
   */
  updateNavigationButtons() {
    if (this.dom.prevUnitBtn) {
      this.dom.prevUnitBtn.disabled = this.state.currentUnitIndex <= 0;
    }

    if (this.dom.nextUnitBtn) {
      this.dom.nextUnitBtn.disabled =
        this.state.currentUnitIndex >= this.state.units.length - 1;
    }
  }

  /**
   * 加载上一个单元