From a939b2afa7a859cb4e809ca4f63870225a6dc6f9 Mon Sep 17 00:00:00 2001
From: Brian Giori <brian.giori@amplitude.com>
Date: Wed, 8 Nov 2023 15:35:25 -0800
Subject: [PATCH] fix: fetch on start by default

---
 __tests__/client.test.ts |  4 ++--
 src/experimentClient.ts  | 33 ++++-----------------------------
 src/types/config.ts      |  7 +++----
 3 files changed, 9 insertions(+), 35 deletions(-)

diff --git a/__tests__/client.test.ts b/__tests__/client.test.ts
index dc90279..ee2b7b7 100644
--- a/__tests__/client.test.ts
+++ b/__tests__/client.test.ts
@@ -922,7 +922,7 @@ describe('start', () => {
     await client.start();
     expect(fetchSpy).toBeCalledTimes(1);
   }, 10000);
-  test('with local evaluation only, does not call fetch', async () => {
+  test('with local evaluation only, calls fetch', async () => {
     const client = new ExperimentClient(API_KEY, {});
     // eslint-disable-next-line @typescript-eslint/ban-ts-comment
     // @ts-ignore
@@ -931,7 +931,7 @@ describe('start', () => {
     };
     const fetchSpy = jest.spyOn(client, 'fetch');
     await client.start();
-    expect(fetchSpy).toBeCalledTimes(0);
+    expect(fetchSpy).toBeCalledTimes(1);
   });
 
   test('with local evaluation only, fetchOnStart enabled, calls fetch', async () => {
diff --git a/src/experimentClient.ts b/src/experimentClient.ts
index 5f3d4e1..1b0681d 100644
--- a/src/experimentClient.ts
+++ b/src/experimentClient.ts
@@ -34,7 +34,6 @@ import {
   isLocalEvaluationMode,
   isNullOrUndefined,
   isNullUndefinedOrEmpty,
-  isRemoteEvaluationMode,
 } from './util';
 import { Backoff } from './util/backoff';
 import {
@@ -149,12 +148,8 @@ export class ExperimentClient implements Client {
    * local flag configurations have been updated, and the {@link fetch()}
    * result has been received (if the request was made).
    *
-   * This function determines whether to {@link fetch()} based on the result of
-   * the flag configurations cached locally or received in the initial flag
-   * configuration response.
-   *
-   * To explicitly force this request to fetch or not, set the
-   * {@link fetchOnStart} configuration option when initializing the SDK.
+   * To force this function not to fetch variants, set the {@link fetchOnStart}
+   * configuration option to `false` when initializing the SDK.
    *
    * Finally, this function will start polling for flag configurations at a
    * fixed interval. To disable polling, set the {@link pollOnStart}
@@ -173,32 +168,12 @@ export class ExperimentClient implements Client {
       this.isRunning = true;
     }
     this.setUser(user);
-    // Get flag configurations, and simultaneously check the local cache for
-    // remote evaluation flags.
     const flagsReadyPromise = this.doFlags();
-    let remoteFlags =
-      this.config.fetchOnStart ??
-      Object.values(this.flags.getAll()).some((flag) =>
-        isRemoteEvaluationMode(flag),
-      );
-    if (remoteFlags) {
-      // We already have remote flags in our flag cache, so we know we need to
-      // evaluate remotely even before we've updated our flags.
+    const fetchOnStart = this.config.fetchOnStart ?? true;
+    if (fetchOnStart) {
       await Promise.all([this.fetch(user), flagsReadyPromise]);
     } else {
-      // We don't know if remote evaluation is required, await the flag promise,
-      // and recheck for remote flags.
       await flagsReadyPromise;
-      remoteFlags =
-        this.config.fetchOnStart ??
-        Object.values(this.flags.getAll()).some((flag) =>
-          isRemoteEvaluationMode(flag),
-        );
-      if (remoteFlags) {
-        // We already have remote flags in our flag cache, so we know we need to
-        // evaluate remotely even before we've updated our flags.
-        await this.fetch(user);
-      }
     }
     if (this.config.pollOnStart) {
       this.poller.start();
diff --git a/src/types/config.ts b/src/types/config.ts
index e1da363..0a0a074 100644
--- a/src/types/config.ts
+++ b/src/types/config.ts
@@ -87,8 +87,7 @@ export interface ExperimentConfig {
    *
    *  - `true`:      fetch will always be called on start.
    *  - `false`:     fetch will never be called on start.
-   *  - `undefined`: the SDK will determine whether to call fetch based on the
-   *                 flags returned in the result.
+   *  - `undefined`: fetch will always be called on start.
    */
   fetchOnStart?: boolean;
 
@@ -145,7 +144,7 @@ export interface ExperimentConfig {
  | **retryFailedAssignment**    | `true` |
  | **automaticExposureTracking** | `true` |
  | **pollOnStart** | `true` |
- | **fetchOnStart** | `undefined` |
+ | **fetchOnStart** | `true` |
  | **automaticFetchOnAmplitudeIdentityChange** | `false` |
  | **userProvider**    | `null` |
  | **analyticsProvider**    | `null` |
@@ -167,7 +166,7 @@ export const Defaults: ExperimentConfig = {
   retryFetchOnFailure: true,
   automaticExposureTracking: true,
   pollOnStart: true,
-  fetchOnStart: undefined,
+  fetchOnStart: true,
   automaticFetchOnAmplitudeIdentityChange: false,
   userProvider: null,
   exposureTrackingProvider: null,