How to use the tui-code-snippet/domUtil/addClass function in tui-code-snippet

disable() {
    addClass(this.el, cls.DISABLED);
  }

highlight() {
    if (!this.isDisabled()) {
      addClass(this.el, cls.HIGHLIGHT);
      this.el.focus();
    }
  }

changeSelected(selected) {
    this.selected = this.nativeEl.selected = selected;
    if (selected) {
      addClass(this.el, SELECTED_CLASS_NAME);
    } else {
      removeClass(this.el, SELECTED_CLASS_NAME);
    }
  }

changeHighlight(highlight) {
    if (highlight) {
      addClass(this.el, HIGHLIGHT_CLASS_NAME);
    } else {
      removeClass(this.el, HIGHLIGHT_CLASS_NAME);
    }
  }

disable() {
    this.disabled = this.nativeEl.disabled = true;
    addClass(this.labelEl, cls.DISABLED);
    this.items.forEach(item => item.disableItemGroup());
  }

makeDisable() {
    this.nativeEl.disabled = true;
    addClass(this.el, cls.DISABLED);
  }

changeDisabled(disabled) {
    if (this.disabled !== disabled) {
      this.disabled = this.nativeEl.disabled = disabled;
      if (disabled) {
        addClass(this.el, DISABLED_CLASS_NAME);
      } else {
        removeClass(this.el, DISABLED_CLASS_NAME);
      }
    }
  }

initializeContainer(manager) {
    manager.appendChild(this.container);

    css(this.container, {
      display: 'none',
      position: 'absolute',
      'z-index': manager.zIndex
    });
    addClass(this.container, 'floating-layer');
  }