fix: front-end improvements

makes some fields visible and other hidden depending on the result of
some API calls, e.g. visitor is logged in -> show "Log out" button

WebApp/ts/generalUseHelpers.ts

@@ -0,0 +1,42 @@
+interface EventData {
+    title: string;
+    location: string;
+    description: string;
+    eventDate: string;
+}
+
+interface MyAccount {
+    userId: number;
+    email: string;
+    firstName: string;
+    lastName: string;
+    createdAt: string;
+    isOrganisation: boolean;
+}
+
+export async function unhideElementById(document: Document, e: string) {
+    var element = document.getElementById(e);
+    if (element) {
+        element.classList.remove('hidden-before-load');
+        console.log(element.classList);
+    }
+}
+
+export async function getEvent(id: string): Promise<EventData> {
+    const res = await fetch("/api/events/" + id);
+    if (!res.ok) {
+        throw Error("To wydarzenie nie istnieje");
+    }
+    const events = await res.json();
+    return events;
+}
+
+export async function getMyAccount(): Promise<MyAccount> {
+    const res = await fetch("/api/auth/my_account");
+    if (!res.ok) {
+        throw Error("U¿ytkownik niezalogowany!");
+    }
+    const data = await res.json();
+    return data;
+}
+