added connection handling to tileset loading

public/js/connectToAPI.js

@@ -290,11 +290,25 @@ var tileset = null
 var tilesetURL = 'http://vm24.fkc.hft-stuttgart.de:8081/CampusLOD2/CityModel/tileset.json';
 
 
-//fetching the tileset
-async function fetchTileset(){
-    const response = await fetch(tilesetURL);
-    const tilesetJSON = await response.json();
-    return tilesetJSON;
+//fetching the tileset and handling the connection
+async function fetchTileset(){   
+
+    fetch(tilesetURL).then((response)=>{        
+        if(response.status >= 200 && response.status<=299){ //successful connection
+            const tilesetJSON =  response.json();     
+            swal({text:"",timer:100}); //used to remove the waiting alert      
+            return tilesetJSON; //returning the tileset            
+        }else{            
+            throw Error(response.statusText);   //throwing an error when a connection is not possible
+        }
+    }).then((jsonResponse)=>{
+        console.log("Tileset"+jsonResponse);
+    }).catch((error)=>{ //catching the error and displaying an alert for the user
+        var errorString = error["stack"]+"\n"+error["message"]; // formatting the error array
+        swal("Could not connect to Server",errorString , "error"); 
+    });
+
+    swal({text:"Connecting to Server ... Please wait !",icon:"info" ,buttons: false}); //displays waiting alert
 }
 
 
@@ -311,32 +325,26 @@ function loadTileset() {
     viewer.scene.primitives.remove(tileset)
     tileContent = []
     modal.style.display = "block";
-
+    
     fetchTileset().then(tilesetJSON =>{       
         tileData = tilesetJSON;
     });
    
 
     var userurl = document.getElementById("3Durl").value;
-    console.log(userurl);
+    // console.log(userurl);
     
     tileset=viewer.scene.primitives.add(new Cesium.Cesium3DTileset({
         url: tilesetURL
     }));
-    console.log(tileset);
+    // console.log(tileset);
 
     viewer.zoomTo(tileset, new Cesium.HeadingPitchRange(0, -0.5, 0));
             modal.style.display = "none";
             saveTilesetContent(tileset)
             deleteTilesetButtons()
 
-    /*
-    tileData.collections.forEach(c => {
-        if (userurl === 'hftcampus' && c.id === "HftCampus") useContent(c.content)
-        if (userurl === 'paderborn' && c.id === "Paderborn") useContent(c.content)
-    })*/
-    console.log(tileData);
-    
+    // console.log(tileData);   
    
 }