Added ServerHttpService.js, Constants.js, ExampleService.js, and changed...

Added ServerHttpService.js, Constants.js, ExampleService.js, and changed HelloWorld.vue for show examples.
The front to back end connection is ready.

FrontendFolder/switch-room/src/services/ServerHttpService.js

+/**
+ * This class will handle the http request that send to server. 
+ * It will help debuging and handle cookie if needed.
+ */
+
+import Constants from "@/services/Constants";
+
+export default{
+
+    Get(path){
+        let url = Constants.Server_URL + path;
+        console.log("GET from: " + url);
+
+        return fetch(url,{
+            method: "GET"
+        })
+            .then((response) =>{
+                if(response.ok){
+                  return response.json();  
+                }
+                throw new Error("Unable to receive GET request from server with url:" + url);
+            })
+            .catch((reason) =>{
+                console.log("Error on GET request", reason);
+            }); 
+    },
+
+    Post(path, bodyData){
+        let url = Constants.Server_URL + path;
+        console.log("POST from: " + url);
+        return fetch(url,{
+            method: "POST",
+            headers: {
+                'Content-Type': 'application/json'
+            },
+            body: JSON.stringify(bodyData)
+        })
+        .then((response)=>{
+            if(response.ok){
+                return response.json();
+            }
+            throw new Error("Unable to receive POST request from server with url:" + url);
+        })
+        .catch((reason) =>{
+            console.log("Error on POST request", reason);
+        }); 
+    }, 
+
+    Put(path, bodyData){
+        let url = Constants.Server_URL + path;
+        console.log("PUT from: " + url);
+        return fetch(url,{
+            method: "PUT",
+            headers: {
+                'Content-Type': 'application/json'
+            },
+            body: JSON.stringify(bodyData)
+        })
+        .then((response)=>{
+            if(response.ok){
+                return response.json();
+            }
+            throw new Error("Unable to receive PUT request from server with url:" + url);
+        })
+        .catch((reason) =>{
+            console.log("Error on PUT request", reason);
+        }); 
+    }, 
+
+    Delete(path){
+        let url = Constants.Server_URL + path;
+        console.log("Delete from: " + url);
+        return fetch(url,{
+            method: "Delete",
+        })
+        .then((response)=>{
+            if(response.ok){
+                return response.json();
+            }
+            throw new Error("Unable to receive DELETE request from server with url:" + url);
+        })
+        .catch((reason) =>{
+            console.log("Error on DELETE request", reason);
+        }); 
+    }, 
+}
+
+/*
+Change logs:
+Date        |       Author          |   Description
+2022-10-12  |    Fangzheng Zhang    |    create class and init
+
+ */
\ No newline at end of file