Case 4- sibling node operation

<! DOCTYPE HTML > 
< HTML lang = "EN" > 
< head > 
  < Meta charset = "UTF-. 8" > 
  < title > the Document </ title > 
</ head > 
< body > 
  < div ID = "Box" > 
    < div > this is a region. 1 </ div > 
    < div > this is a region 2 </ div > 
    <div id="c3">This is a region. 3 </ div > 
    < div > This is a region. 4 </ div > 
    < div > This is a region. 5 </ div > 
  </ div > 
  < Script > 
    var C3 = document.getElementById ( ' C3 ' ); 

    // the nextSibling next sibling node 
    // next sibling element nextElementSibling 
    //  
    // sibling node previousSibling 
    // sibling elements on previousElementSibling 
    // the console.log (c3.nextSibling); 
    // console.log(c3.previousSibling);
    // 
    // console.log(c3.nextElementSibling);
    // console.log(c3.previousElementSibling);


    console.log(getNextElementSibling(c3));
    // 获取下一个兄弟元素
   function getNextElementSibling(element) {
      var el = element;
      while (el = el.nextSibling) {
        if (el.nodeType === 1) {
            return el;
        }
      }
      return null;
    }
  </script>
</body>
</html>