Javascript 在移动视图上单击显示下拉列表

我的导航栏上有一个下拉菜单。我希望它在大屏幕上显示为悬停，但在小屏幕上显示为单击

         <nav class="site-navigation position-relative text-right" role="navigation">

          <ul class="site-menu main-menu js-clone-nav mr-auto d-none d-lg-block">
            <li><a href="index.html" class="nav-link">Home</a></li>
            <li><a href="about-us.html" class="nav-link">About Us</a></li>
            <li><a href="products.html" class="nav-link">Products</a></li>
            <li class="has-children"><a href="" class="nav-link" disabled>Services</a>
            <ul class="dropdown">
            <li><a href="physical-design-assistance.html" class="nav-link">Physical 
             Design & Assistance</a></li>
            <li><a href="system-development.html" class="nav-link active">System 
             Development</a></li>
            <li><a href="clock-development.html" class="nav-link">Clock 
              Development</a></li>
            </ul>
            </li>
            <li><a href="careers.html" class="nav-link">Careers</a></li>
            <li><a href="contact-us.html" class="nav-link">Contact Us</a></li>
          </ul>
          </nav>

---

请更新您的代码，使其更具可操作性。同时添加您的CSS和JS，这样其他人可以帮助您使用itAn，如果围绕您的addEventListeners的语句带有屏幕宽度的条件将是一个简单的解决方案，请为您提供的上述html代码添加相关的CSS代码

      .site-navbar .site-navigation .site-menu .has-children {
       position: relative; }
    .site-navbar .site-navigation .site-menu .has-children > a {
    position: relative;
    padding-right: 20px; }
    .site-navbar .site-navigation .site-menu .has-children > a:before {
      position: absolute;
      content: "\e313";
      font-size: 16px;
      top: 50%;
      right: 0;
      -webkit-transform: translateY(-50%);
      -ms-transform: translateY(-50%);
      transform: translateY(-50%);
      font-family: 'icomoon';
       }
    .site-navbar .site-navigation .site-menu .has-children .dropdown {
    visibility: hidden;
    opacity: 0;
    top: 100%;
    position: absolute;
    text-align: left;

    -webkit-box-shadow: 0 2px 10px -2px rgba(0, 0, 0, 0.1);
    box-shadow: 0 2px 10px -2px rgba(0, 0, 0, 0.1);
    border-left: 1px solid #edf0f5;
    border-right: 1px solid #edf0f5;
    border-bottom: 1px solid #edf0f5;
    padding: 0;
    margin-top: 20px;
    margin-left: 0;
    background: #f5f5f5;
    -webkit-transition: 0.2s 0s;
    -o-transition: 0.2s 0s;
    transition: 0.2s 0s; }
    .site-navbar .site-navigation .site-menu .has-children .dropdown.arrow-top {
      position: absolute; }
      .site-navbar .site-navigation .site-menu .has-children .dropdown.arrow-top:before {
        bottom: 100%;
        left: 20%;
        border: solid transparent;
        content: " ";
        height: 0;
        width: 0;
        position: absolute;
        pointer-events: none; }
      .site-navbar .site-navigation .site-menu .has-children .dropdown.arrow-top:before {
        border-color: rgba(136, 183, 213, 0);
        border-bottom-color: #fff;
        border-width: 10px;
        margin-left: -10px; }
    .site-navbar .site-navigation .site-menu .has-children .dropdown a {
      text-transform: none;
      letter-spacing: normal;
      -webkit-transition: 0s all;
      -o-transition: 0s all;
      transition: 0s all;
      color: #333; }
    .site-navbar .site-navigation .site-menu .has-children .dropdown 
       .active > a {
      color: #e6ae48 !important; }
    .site-navbar .site-navigation .site-menu .has-children .dropdown > li 
      {
      list-style: none;
      padding: 0;
      margin: 0;
      min-width: 200px; }
      .site-navbar .site-navigation .site-menu .has-children .dropdown > 
         li > a {
        padding: 9px 20px;
        display: block; 
        }
        .site-navbar .site-navigation .site-menu .has-children .dropdown > 
         li > a:hover {
          background: #28699c;
          color: #fff !important; }
      .site-navbar .site-navigation .site-menu .has-children .dropdown > 
        li.has-children > a:before {
        content: "\e315";
        right: 20px; }
      .site-navbar .site-navigation .site-menu .has-children .dropdown > 
         li.has-children > .dropdown, .site-navbar .site-navigation .site- 
         menu .has-children .dropdown > li.has-children > ul {
        left: 100%;
        top: 0; }
      .site-navbar .site-navigation .site-menu .has-children .dropdown > 
          li.has-children:hover > a, .site-navbar .site-navigation .site- 
        menu .has-children .dropdown > li.has-children:active > a, .site- 
        navbar .site-navigation .site-menu .has-children .dropdown > 
         li.has-children:focus > a {
        background: #f4f5f9;
        color: #25262a; }
  .site-navbar .site-navigation .site-menu .has-children:hover > a, .site-navbar .site-navigation .site-menu .has-children:focus > a, .site-navbar .site-navigation .site-menu .has-children:active > a {
    color: #fff; }
  .site-navbar .site-navigation .site-menu .has-children:hover, .site-navbar .site-navigation .site-menu .has-children:focus, .site-navbar .site-navigation .site-menu .has-children:active {
    cursor: pointer; }
    .site-navbar .site-navigation .site-menu .has-children:hover > .dropdown, .site-navbar .site-navigation .site-menu .has-children:focus > .dropdown, .site-navbar .site-navigation .site-menu .has-children:active > .dropdown {
      -webkit-transition-delay: 0s;
      -o-transition-delay: 0s;
      transition-delay: 0s;
      margin-top: 0px;
      visibility: visible;
      opacity: 1; }