narrow: Add helper to check allowed web public narrow.

Adds a helper function to check whether a narrow is an allowed
web public narrow or not.

web/src/filter.ts

@@ -865,7 +865,7 @@ export class Filter {
             if (term.operand === undefined) {
                 return false;
             }
-            if (!hash_parser.allowed_web_public_narrow_operators.includes(term.operator)) {
+            if (!hash_parser.is_an_allowed_web_public_narrow(term.operator)) {
                 return false;
             }
         }

web/src/hash_parser.ts

@@ -116,6 +116,10 @@ export function is_in_specified_hash_category(hash_categories: string[]): boolea
     return hash_categories.includes(main_hash);
 }
 
+export function is_an_allowed_web_public_narrow(operator: string): boolean {
+    return allowed_web_public_narrow_operators.includes(operator);
+}
+
 export const allowed_web_public_narrow_operators = [
     "channels",
     "channel",
@@ -157,7 +161,7 @@ export function is_spectator_compatible(hash: string): boolean {
 
     if (main_hash === "narrow") {
         const hash_section = get_hash_section(hash);
-        if (!allowed_web_public_narrow_operators.includes(hash_section)) {
+        if (!is_an_allowed_web_public_narrow(hash_section)) {
             return false;
         }
         return true;

web/src/message_view.ts

@@ -444,8 +444,7 @@ export let show = (raw_terms: NarrowTerm[], show_opts: ShowMessageViewOpts): voi
         // policy?
         !is_combined_feed_global_view &&
         raw_terms.some(
-            (raw_term) =>
-                !hash_parser.allowed_web_public_narrow_operators.includes(raw_term.operator),
+            (raw_term) => !hash_parser.is_an_allowed_web_public_narrow(raw_term.operator),
         )
     ) {
         spectators.login_to_access();