切换菜单，一次使用纯JavaScript打开一个菜单

var navclick = document.getElementsByClassName("js-dropdown");
var navContent = document.getElementsByClassName('-arrow-link-content');
for (var i = 0; i < navclick.length; i++) {
    navclick[i].onclick = function () {
      if (this.parentNode.querySelector('div.-arrow-link-content').classList.contains('nav-active')) {
        this.parentNode.querySelector('div.-arrow-link-content').classList.remove('nav-active'); 
      }
      else {
        try {
          // if an open element exists, close it first
          this.parentNode.parentNode.querySelector('.nav-active').classList.remove('nav-active');
         }
          catch (error){ 
            // Error occurs when no open elment exists, in that case: Do nothing
          }
        this.parentNode.querySelector('div.-arrow-link-content').classList.add('nav-active');
      }
    }
  }
 

.-arrow-link-content {
  display:none;
}
.nav-active{ display:block;}

<ul class="c-icons" id="c-iconslist">
                    <li>
                        <div class="c-icons__text js-dropdown">heading 1</div>
                     <div class="c-icons__textdropdown -arrow-link-content"> Content 1</div>
                    </li>
                       <li>
                        <div class="c-icons__text js-dropdown">heading 2</div>
                     <div class="c-icons__textdropdown -arrow-link-content"> Content 2</div>
                    </li>
                </ul>