Migrating some files from javascript to typescript (#24663)

* Migrating some files to typescript

* Some other files migrated

* Migrating more javascript to typescript

* Migrating more javascript to typescript

* Fixing types

* Fixing linter errors

* Fixing some imports

* Fixing linter errors

* Renaming the snapshots

* Addressing PR review comments

webapp/channels/src/tests/helpers/localstorage.tsx

@@ -3,6 +3,8 @@
 
 // Based on https://stackoverflow.com/a/41434763
 class LocalStorageMock {
+    store: {[key: string]: string};
+
     constructor() {
         this.store = {};
     }
@@ -11,17 +13,19 @@ class LocalStorageMock {
         this.store = {};
     }
 
-    getItem(key) {
+    getItem(key: string): string | null {
         return this.store[key] || null;
     }
 
-    setItem(key, value) {
+    setItem(key: string, value: {toString: () => string}) {
         this.store[key] = value.toString();
     }
 
-    removeItem(key) {
+    removeItem(key: string) {
         delete this.store[key];
     }
 }
 
-global.localStorage = new LocalStorageMock();
+(global as any).localStorage = new LocalStorageMock();
+
+export {};

webapp/channels/src/tests/helpers/user_agent_mocks.ts

@@ -20,7 +20,7 @@ Object.defineProperty(window.navigator, 'userAgent', {
 export function reset() {
     set(initialUA);
 }
-export function set(ua) {
+export function set(ua: string) {
     currentUA = ua;
 }
 export function mockSafari() {