Refactor net.html to extract the creation of main div into a separate…

… function and dispose the previous chart instance

rust_http_proxy/html/net.html

@@ -55,7 +55,7 @@ <h1 class="in"></h1>
             newMainDiv.className = 'out';
             // 将新的 main div 添加到文档中
             document.body.appendChild(newMainDiv);
-
+            myChart.dispose();
             myChart = null;
             return newMainDiv;
         }