js如何制作放大效果的图片

<th><i class=""></i>车系展示图：</th><td>   <i><img id = "img" class="lazyload" src="data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAYAAAAfFcSJAAAAAXNSR0IArs4c6QAAAARnQU1BAACxjwv8YQUAAAAJcEhZcwAADsQAAA7EAZUrDhsAAAANSURBVBhXYzh8+PB/AAffA0nNPuCLAAAAAElFTkSuQmCC" data-original="图片.jpg"   onclick="fun()"><br></i>   <p>点击可放大图片</p></td>

这是javascript部分

<script type="text/javascript">   function fun(){      var submitSpan = document.getElementById("img");      submitSpan.style.width = '600px';      submitSpan.style.height = '400px';      submitSpan.onclick = function () {         fun1();      }   }   function fun1(){      var submitSpan = document.getElementById("img");      submitSpan.style.width = '150px';      submitSpan.style.height = '100px';      submitSpan.onclick = function () {         fun();      }   }  </script>