Keep the value of config from becoming null

src/utils/config/__tests__/load-config.spec.ts

@@ -1,5 +1,6 @@
-import { afterEach, describe, expect, it, vi } from "vitest";
+import { describe, it, expect, vi, afterEach } from "vitest";
 import { useLoadConfigT } from "../load-config";
+import { nextTick } from "vue";
 
 globalThis.fetch = vi.fn();
 
@@ -12,13 +13,14 @@ const createResponse = (data: any): Response =>
     statusText: "OK",
   }) as Response;
 
-const response404 = {
-  json: () => new Promise((resolve) => resolve({})),
-  clone: () => response404,
-  ok: false,
-  status: 404,
-  statusText: "Not Found",
-} as Response;
+const createErrorResponse = (status: number, statusText: string): Response =>
+  ({
+    json: () => Promise.reject(new Error(statusText)),
+    clone: () => createErrorResponse(status, statusText),
+    ok: false,
+    status,
+    statusText,
+  }) as Response;
 
 type Config = {
   apiUrl: string;
@@ -33,7 +35,6 @@ const defaultConfig = {
 const validateConfig = (config: Config) => {
   if (typeof config.apiUrl !== "string") throw Error("apiUrl is not string");
   if (config?.apiUrl === "") throw Error("apiUrl is empty");
-
   if (typeof config.apiVersion !== "number") throw Error("apiVersion is not number");
 };
 
@@ -42,65 +43,119 @@ describe("useLoadConfigT", () => {
     vi.mocked(globalThis.fetch).mockReset();
   });
 
-  it("should return data", async () => {
+  it("should return data on successful initial fetch", async () => {
     const responseData = {
       apiUrl: "http://example.com/api",
       apiVersion: 2.0,
     };
-    const expected = { ...responseData };
-    vi.mocked(fetch).mockResolvedValue(createResponse(responseData));
-    const { config, loading, error } = await useLoadConfigT<Config>();
+    vi.mocked(fetch).mockResolvedValueOnce(createResponse(responseData));
+
+    const { config, loading, error, execute } = await useLoadConfigT<Config>(
+      defaultConfig,
+      validateConfig
+    );
     expect(loading.value).toBe(false);
     expect(error.value).toBeUndefined();
-    expect(config.value).toEqual(expected);
+    expect(config.value).toEqual(responseData);
+    expect(execute).toBeDefined();
   });
 
-  it("should return 404 error", async () => {
-    vi.mocked(fetch).mockResolvedValue(response404);
-    const { config, loading, error } = await useLoadConfigT<Config>();
-    expect(loading.value).toBe(false);
-    expect(error.value).toEqual("Not Found");
-    expect(config.value).toBeNull();
+  it("should throw error on initial fetch failure", async () => {
+    vi.mocked(fetch).mockResolvedValueOnce(createErrorResponse(404, "Not Found"));
+
+    await expect(useLoadConfigT<Config>(defaultConfig, validateConfig)).rejects.toThrow(
+      "Failed to load config: undefined"
+    );
   });
 
-  it("should merge with default", async () => {
-    const responseData = {
+  it("should not throw error on subsequent fetch failure, update error.value, and keep old config", async () => {
+    const initialData = {
+      apiUrl: "http://example.com/api",
       apiVersion: 2.0,
     };
-    const expected = { ...defaultConfig, ...responseData };
-    vi.mocked(fetch).mockResolvedValue(createResponse(responseData));
-    const { config, loading, error } = await useLoadConfigT<Config>(defaultConfig);
+    vi.mocked(fetch)
+      .mockResolvedValueOnce(createResponse(initialData))
+      .mockResolvedValueOnce(createErrorResponse(500, "Internal Server Error"));
+
+    const { config, loading, error, execute } = await useLoadConfigT<Config>(
+      defaultConfig,
+      validateConfig
+    );
+    expect(config.value).toEqual(initialData);
+
+    await execute();
+    await nextTick();
+
+    expect(config.value).toEqual(initialData); // Config should remain unchanged
     expect(loading.value).toBe(false);
-    expect(error.value).toBeUndefined();
-    expect(config.value).toEqual(expected);
+    expect(error.value).toBeDefined();
+    expect(error.value).toBe("Internal Server Error");
   });
 
-  it("should validate", async () => {
-    const responseData = {
+  it("should update config on successful subsequent fetch", async () => {
+    const initialData = {
+      apiUrl: "http://example.com/api",
       apiVersion: 2.0,
     };
-    const expected = { ...defaultConfig, ...responseData };
-    vi.mocked(fetch).mockResolvedValue(createResponse(responseData));
-    const { config, loading, error } = await useLoadConfigT<Config>(
+    const updatedData = {
+      apiUrl: "http://example.com/api/v2",
+      apiVersion: 3.0,
+    };
+    vi.mocked(fetch)
+      .mockResolvedValueOnce(createResponse(initialData))
+      .mockResolvedValueOnce(createResponse(updatedData));
+
+    const { config, loading, error, execute } = await useLoadConfigT<Config>(
       defaultConfig,
       validateConfig
     );
+    expect(config.value).toEqual(initialData);
+
+    await execute();
+    await nextTick();
+
+    expect(config.value).toEqual(updatedData);
     expect(loading.value).toBe(false);
     expect(error.value).toBeUndefined();
-    expect(config.value).toEqual(expected);
   });
 
-  it("should return validation error", async () => {
+  it("should throw validation error on initial fetch", async () => {
     const responseData = {
       apiUrl: "",
+      apiVersion: 2.0,
     };
-    vi.mocked(fetch).mockResolvedValue(createResponse(responseData));
-    const { config, loading, error } = await useLoadConfigT<Config>(
+    vi.mocked(fetch).mockResolvedValueOnce(createResponse(responseData));
+
+    await expect(useLoadConfigT<Config>(defaultConfig, validateConfig)).rejects.toThrow(
+      "Failed to load config: apiUrl is empty"
+    );
+  });
+
+  it("should not throw validation error on subsequent fetch, update error.value, and keep old config", async () => {
+    const initialData = {
+      apiUrl: "http://example.com/api",
+      apiVersion: 2.0,
+    };
+    const invalidData = {
+      apiUrl: "",
+      apiVersion: 3.0,
+    };
+    vi.mocked(fetch)
+      .mockResolvedValueOnce(createResponse(initialData))
+      .mockResolvedValueOnce(createResponse(invalidData));
+
+    const { config, loading, error, execute } = await useLoadConfigT<Config>(
       defaultConfig,
       validateConfig
     );
+    expect(config.value).toEqual(initialData);
+
+    await execute();
+    await nextTick();
+
+    expect(config.value).toEqual(initialData); // Config should remain unchanged
     expect(loading.value).toBe(false);
-    expect(error.value?.message).toEqual("apiUrl is empty");
-    expect(config.value).toBeNull();
+    expect(error.value).toBeDefined();
+    expect(error.value?.message).toBe("apiUrl is empty");
   });
 });

src/utils/config/load-config.ts

@@ -1,7 +1,39 @@
 import { useFetch } from "@vueuse/core";
 import * as path from "path";
-import { computed, ref } from "vue";
+import type { ShallowRef } from "vue";
+import { computed, ref, shallowRef, watchEffect } from "vue";
 
+/**
+ * Asynchronously loads and manages a configuration object with validation and error handling.
+ *
+ * @template - The type of the configuration object, must extend object.
+ * @param - The default configuration object to use as a base.
+ * @param - A function to validate the configuration object.
+ *
+ * @returns
+ *   - loading: A computed ref indicating whether the config is currently loading.
+ *   - error: A ref containing any fetch or validation errors.
+ *   - config: A shallow ref containing the current valid configuration.
+ *   - execute: A function to manually trigger a config refresh.
+ *
+ * @throws Throws an error if the initial fetch fails or if validation fails on the initial fetch.
+ *
+ * @description
+ * This function fetches a configuration object from a URL, merges it with a default config,
+ * validates it, and provides reactive references to the resulting data and state.
+ * It handles both initial and subsequent fetches, with different error behaviors for each:
+ * - On initial fetch: Throws an error if fetch fails or validation fails.
+ * - On subsequent fetches: Updates error state but doesn't throw, keeps old config if validation fails.
+ *
+ * @example
+ * ```typescript
+ * const { config, loading, error, execute } = await useLoadConfigT(defaultConfig, validateConfig);
+ * // Use config.value to access the current configuration
+ * // Use loading.value to check if a fetch is in progress
+ * // Use error.value to check for any errors
+ * // Call execute() to manually refresh the configuration
+ * ```
+ */
 export async function useLoadConfigT<T extends object>(
   defaultConfig: Partial<T> = {},
   validate: (config: T) => void = () => true
@@ -12,37 +44,56 @@ export async function useLoadConfigT<T extends object>(
     data,
     error: fetchError,
     isFinished,
+    execute,
   } = await useFetch<T>(configUrl, { refetch: true }).json<T>();
 
-  // Initially false because of await. Can be true if configUrl is changed.
+  // Initially false because of await. Can become true later.
   const loading = computed(() => !isFinished.value);
 
-  // null until data is loaded
   const toBeValidated = computed<T | null>(
     () => data.value && { ...defaultConfig, ...(data.value ?? {}) }
   );
 
-  const validationError = computed(() => {
-    if (loading.value) return;
-    if (!toBeValidated.value) return;
-    try {
-      validate(toBeValidated.value);
-    } catch (e: unknown) {
-      // console.error(e);
-      return e as Error;
-    }
-  });
-
-  const error = computed(
-    () => (fetchError.value as Error | undefined) || validationError.value
+  const validationError = ref<Error | undefined>(undefined);
+  const error = ref<Error | undefined>(undefined);
+  let validConfig!: ShallowRef<T> | undefined;
+  watchEffect(
+    () => {
+      if (loading.value) return;
+      if (toBeValidated.value) {
+        try {
+          validate(toBeValidated.value);
+          validationError.value = undefined;
+        } catch (e: unknown) {
+          validationError.value = e as Error;
+        }
+      }
+      error.value = (fetchError.value as Error | undefined) || validationError.value;
+      if (error.value) return;
+      const rawValidConfig = toBeValidated.value;
+      if (rawValidConfig === null) return;
+      if (validConfig === undefined) {
+        validConfig = shallowRef<T>(rawValidConfig);
+      } else {
+        validConfig.value = rawValidConfig;
+      }
+    },
+    { flush: "sync" }
   );
 
-  const config = computed<T | null>(() => (error.value ? null : toBeValidated.value));
+  if (error.value) {
+    throw Error(`Failed to load config: ${error.value.message}`);
+  }
+
+  if (validConfig === undefined) {
+    throw Error("The config is undefined while no error occurred.");
+  }
 
   return {
     loading,
     error,
-    config,
+    config: validConfig,
+    execute,
   };
 }