Make useGetClassName not a hook

src/lib/useGetClassName.ts

@@ -1,24 +1,63 @@
 import { clsx } from "keycloakify/tools/clsx";
-import { useConstCallback } from "keycloakify/tools/useConstCallback";
+import type { Param0 } from "tsafe";
+
+// NOTE: Note for people trying to implement Keycloakify in other frontend
+// frameworks. This can be used outside of React, useGetClassName isn't actually a hook.
 
 export function createUseClassName<ClassKey extends string>(params: {
     defaultClasses: Record<ClassKey, string | undefined>;
 }) {
     const { defaultClasses } = params;
 
+    function areSameParams(
+        params1: Param0<typeof useGetClassName>,
+        params2: Param0<typeof useGetClassName>
+    ): boolean {
+        if (params1.doUseDefaultCss !== params2.doUseDefaultCss) {
+            return false;
+        }
+
+        if (params1.classes === params2.classes) {
+            return true;
+        }
+
+        return JSON.stringify(params1.classes) === JSON.stringify(params2.classes);
+    }
+
+    let cache:
+        | {
+              params: Param0<typeof useGetClassName>;
+              result: ReturnType<typeof useGetClassName>;
+          }
+        | undefined = undefined;
+
     function useGetClassName(params: {
         doUseDefaultCss: boolean;
         classes: Partial<Record<ClassKey, string>> | undefined;
-    }) {
-        const { classes, doUseDefaultCss } = params;
+    }): { getClassName: (classKey: ClassKey) => string } {
+        // NOTE: We implement a cache here only so that getClassName can be stable across renders.
+        // We don't want to use useConstCallback because we want this to be useable outside of React.
+        use_cache: {
+            if (cache === undefined) {
+                break use_cache;
+            }
 
-        const getClassName = useConstCallback((classKey: ClassKey): string => {
+            if (!areSameParams(cache.params, params)) {
+                break use_cache;
+            }
+
+            return cache.result;
+        }
+
+        function getClassName(classKey: ClassKey): string {
             return clsx(
                 classKey,
-                doUseDefaultCss ? defaultClasses[classKey] : undefined,
-                classes?.[classKey]
+                params.doUseDefaultCss ? defaultClasses[classKey] : undefined,
+                params.classes?.[classKey]
             );
-        });
+        }
+
+        cache = { params, result: { getClassName } };
 
         return { getClassName };
     }