feat: 调整加载方式

public/index.html

@@ -210,21 +210,34 @@
         </div>
 	</div>
   <script>
-    function downloadJs(url){
+    function downloadJs(url, callback){
       var script = document.createElement('script');
       script.type = 'text/javascript'
+      if(script.readyState){  //IE
+        script.onreadystatechange = function(){
+            if (script.readyState == "loaded" ||
+                script.readyState == "complete"){
+                script.onreadystatechange = null;
+                if(callback) callback();
+            }
+        };
+    } else {  //Others
+        script.onload = function(){
+          if(callback) callback();
+        };
+    }
       script.src = url;
       document.body.appendChild(script);
     }
     window.onload = function(){
       console.log('window.onload')
-      downloadJs('./lib/sycim/sycim.min.js');
+      downloadJs('./lib/sycim/sycim.min.js', () => {
         setTimeout(() => {
-
           window.Cesium = sycim.Cesium;
           sycim.config.baseUrl = "./lib/sycim/resources/";
           downloadJs('./lib/SuperMap3D/SuperMap3D.js');
         }, 500);
+      });
     }
   </script>
   </body>