Added checkFetchStatus function and fetch will use it.

client/funcs/checkFetchStatus.js

@@ -0,0 +1,7 @@
+module.exports = function (response) {
+    if (response.ok) { // res.status >= 200 && res.status < 300
+        return response;
+    } else {
+        throw new Error(response.status + " " + response.statusText);
+    }
+}