Prevent params from being changed

Author: kahirokunn

src/apis/computed.ts

@@ -11,9 +11,11 @@ interface Option<T> {
 // read-only
 export function computed<T>(getter: Option<T>['get']): Readonly<Ref<Readonly<T>>>;
 // writable
-export function computed<T>(options: Option<T>): Ref<T>;
+export function computed<T>(options: Option<T>): Ref<Readonly<T>>;
 // implement
-export function computed<T>(options: Option<T>['get'] | Option<T>): Ref<T> {
+export function computed<T>(
+  options: Option<T>['get'] | Option<T>
+): Readonly<Ref<Readonly<T>>> | Ref<Readonly<T>> {
   const vm = getCurrentVM();
   let get: Option<T>['get'], set: Option<T>['set'] | undefined;
   if (typeof options === 'function') {