feat: Add FDv2 DataManager and enable experimental FDv2 support. by kinyoklion · Pull Request #1161 · launchdarkly/js-core

kinyoklion · 2026-03-06T22:17:35Z

Connects together most of the FDv2 components we have with an FDv2 DataManager. The configuration is @internal and will remain that way until we are ready for consumers.

Doesn't:
This doesn't yet address the public API changes for being able to directly set a connection mode.
It doesn't add support for custom modes.
It doesn't add the inputs to the automatic mode switching.
Contract tests (unless Todd adds them and this comment becomes irrelevant.

Does:
Connect together F2v2 E2E.
Adds the the data manager.
Includes the mode debouncing.

Note

High Risk
High risk because it introduces a new FDv2 data-management path (mode resolution, polling/streaming orchestration, FDv1 fallback) and conditionally switches the browser SDK to new endpoints based on dataSystem, which can impact flag delivery and streaming behavior.

Overview
Adds an FDv2 DataManager implementation (createFDv2DataManagerBase) that owns connection-mode resolution, debounced lifecycle/network transitions, FDv2 data source orchestration, and optional FDv1 polling fallback.

Updates the browser SDK to opt into FDv2 when configuration.dataSystem is present: it builds FDv2 query params, selects FDv2 polling endpoints, wires listener-driven streaming via optional DataManager hooks, and triggers immediate event flushing on background transitions.

Tightens FDv2 mode-table typing/validation by separating initializers vs synchronizers (disallowing cache as a synchronizer) and expands exports/tests accordingly; also tweaks FDv2 synchronizer fallback logging and updates examples/CI package size thresholds.

^{Written by Cursor Bugbot for commit 304e5f3. This will update automatically on new commits. Configure here.}

github-actions · 2026-03-06T22:19:04Z

@launchdarkly/js-sdk-common size report
This is the brotli compressed size of the ESM build.
Compressed size: 25661 bytes
Compressed size limit: 29000
Uncompressed size: 126143 bytes

github-actions · 2026-03-06T22:19:23Z

@launchdarkly/browser size report
This is the brotli compressed size of the ESM build.
Compressed size: 178822 bytes
Compressed size limit: 194000
Uncompressed size: 828026 bytes

github-actions · 2026-03-06T22:19:27Z

@launchdarkly/js-client-sdk size report
This is the brotli compressed size of the ESM build.
Compressed size: 31069 bytes
Compressed size limit: 34000
Uncompressed size: 110826 bytes

kinyoklion · 2026-03-06T22:21:59Z

packages/sdk/browser/src/options.ts

+   * the new `/sdk/poll/eval` and `/sdk/stream/eval` endpoints with the
+   * FDv2 protocol handler and orchestrator.
+   *
+   * Default: false


Suggested change

* Default: false

* @hidden

* Default: false

Add `dataSystem` option to LDOptions for FDv2 data system configuration. The field is marked @internal and stripped from public type declarations via stripInternal. When present, ConfigurationImpl deep-validates it using dataSystemValidators with platform-specific defaults passed via LDClientInternalOptions.dataSystemDefaults. - Browser SDK passes BROWSER_DATA_SYSTEM_DEFAULTS - React Native SDK passes MOBILE_DATA_SYSTEM_DEFAULTS - No behavioral changes — the configuration is accepted and validated but not yet wired to any data manager selection logic SDK-1935

Convert validators from a static constant to a createValidators() factory function that accepts platform-specific dataSystemDefaults. When defaults are provided, dataSystem uses validatorOf() with built-in defaults for deep nested validation in a single pass. Add builtInDefaults parameter to validatorOf() so the compound validator carries its own defaults without relying on parent-level defaults (which would leak into the result for absent fields). Remove the separate deep-validation block from ConfigurationImpl — the generic validateOptions call now handles everything. Add tests for non-object dataSystem, granular automaticModeSwitching, and no-leakage of dataSystem defaults to other config fields.

github-actions · 2026-03-10T23:23:32Z

@launchdarkly/js-client-sdk-common size report
This is the brotli compressed size of the ESM build.
Compressed size: 36171 bytes
Compressed size limit: 38000
Uncompressed size: 199479 bytes

Resolved conflicts in sdk-client index.ts (kept FDv2 orchestration exports needed by integration branch) and BrowserClient.ts (kept single-object super() call structure).

Resolved conflict in StreamingFDv2Base.ts: took main's stopped guard and errorInfoFromNetworkError helper, removed unused DataSourceErrorKind import.

kinyoklion · 2026-03-12T21:31:18Z

packages/shared/sdk-client/src/DataManager.ts

   * Closes the data manager. Any active connections are closed.
   */
  close(): void;
+


This may change when we determine how we are going to handle setConnectionMode.

kinyoklion · 2026-03-12T22:53:13Z

packages/sdk/browser/src/BrowserFDv2DataManager.ts

I think, with a few tweaks, we can maybe eliminate this entirely.

kinyoklion · 2026-03-12T23:41:06Z

packages/sdk/browser/example/src/app.ts

We will want to remove this before we commit.

kinyoklion · 2026-03-12T23:41:51Z

packages/shared/sdk-client/src/api/datasource/DataSourceEntry.ts

  readonly endpoints?: EndpointConfig;
 }

+/**


This allows us to exclude cache from being a potential synchronizer.

kinyoklion · 2026-03-12T23:42:14Z

packages/shared/sdk-client/src/datasource/ConnectionModeConfig.ts

 };

-const dataSourceEntryArrayValidator = arrayOf('type', {
+const initializerEntryArrayValidator = arrayOf('type', {


Extend the typing changes to the runtime validation.

kinyoklion · 2026-03-12T23:42:50Z

packages/shared/sdk-client/src/datasource/FDv2DataManagerBase.ts

I feel like there is two much code inside this.

Maybe the majority is just typing, so the volume isn't too bad, but this is a dependency hot-point. Lots of things coming together here.

kinyoklion · 2026-03-13T17:31:02Z

bugbot review

packages/sdk/browser/example/src/app.ts

packages/sdk/browser/src/BrowserFDv2DataManager.ts

kinyoklion · 2026-03-13T17:54:31Z

packages/shared/sdk-client/src/datasource/FDv2DataManagerBase.ts

+      modeDef.initializers
+        // Skip cache when bootstrapped — bootstrap data was applied to the
+        // flag store before identify, so the cache would only load older data.
+        .filter((entry) => !(bootstrapped && entry.type === 'cache'))


We could generalize this, but it feels like a YAGNI situation.

kinyoklion · 2026-03-13T17:55:46Z

packages/shared/sdk-client/src/datasource/FDv2DataManagerBase.ts

+            initializerFactories.push(factory);
+          } else {
+            logger.warn(
+              `${logTag} Unsupported initializer type '${entry.type}'. It will be skipped.`,


The typing, for now, prevents this, but it will be possible with custom modes.

I wonder if it should be an error?

kinyoklion · 2026-03-13T22:49:47Z

packages/shared/sdk-client/src/datasource/FDv2DataManagerBase.ts

+    }
+    if (forcedStreaming === false) {
+      // Explicitly forced off — use configured mode, but never streaming.
+      return initialForegroundMode === 'streaming' ? 'one-shot' : initialForegroundMode;


This is somewhat jank, but maintains the functionality from the existing implementation.

In the future we can remove setStreaming and things will be more logical with setConnectionMode.

kinyoklion · 2026-03-13T22:50:06Z

bugbot review

cursor

✅ Bugbot reviewed your changes and found no new issues!

1 issue from previous review remains unresolved.

Comment @cursor review or bugbot run to trigger another review on this PR

…k/NOTICKET/testing-fdv2

kinyoklion commented Mar 6, 2026

View reviewed changes

kinyoklion force-pushed the mk/NOTICKET/testing-fdv2 branch 2 times, most recently from 5e2b2cb to 4f882ca Compare March 10, 2026 17:03

kinyoklion and others added 9 commits March 10, 2026 14:13

fix: Lint fixes for dataSystem configuration

a90b962

Merge branch 'main' into rlamb/SDK-1935/FDv2-configuration

fa111d5

WIP: Example of this working together

73c6f2a

Fix interrupted state for non-status codes.

109aeea

Tests

e7f5049

Fix basis.

e2821cd

rebase data system config

a7413c0

kinyoklion force-pushed the mk/NOTICKET/testing-fdv2 branch from 4f882ca to a7413c0 Compare March 10, 2026 22:20

Integrate mode switching and caching.

e40b0d5

kinyoklion and others added 9 commits March 11, 2026 13:11

Merge branch 'main' into mk/NOTICKET/testing-fdv2

7bfa7ac

Resolved conflicts in sdk-client index.ts (kept FDv2 orchestration exports needed by integration branch) and BrowserClient.ts (kept single-object super() call structure).

Streaming control interface

e2b7d15

Skip cache when bootstrap is available.

9d242d4

Add event flush on backgrounding.

cee85ee

remove flag_eval support; use flag-eval only

0d92a78

Merge branch 'main' into mk/NOTICKET/testing-fdv2

5ee0469

Remove debug logging from FDv2DataSource.

cfc1207

Commonize stream control input between browser and RN for FDv2.

ea3eb1d

Merge branch 'main' into mk/NOTICKET/testing-fdv2

67eff51

Resolved conflict in StreamingFDv2Base.ts: took main's stopped guard and errorInfoFromNetworkError helper, removed unused DataSourceErrorKind import.

kinyoklion commented Mar 12, 2026

View reviewed changes

kinyoklion added 2 commits March 12, 2026 14:44

Increase package size limits

4f59d39

Don't export internals

c603f56

kinyoklion commented Mar 12, 2026

View reviewed changes

packages/sdk/browser/example/src/app.ts

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We will want to remove this before we commit.

kinyoklion commented Mar 12, 2026

View reviewed changes

Merge branch 'main' into mk/NOTICKET/testing-fdv2

3e287df

cursor bot reviewed Mar 13, 2026

View reviewed changes

packages/sdk/browser/example/src/app.ts Outdated Show resolved Hide resolved

packages/sdk/browser/src/BrowserFDv2DataManager.ts Outdated Show resolved Hide resolved

kinyoklion added 2 commits March 13, 2026 10:46

Remove browser specific data manager.

bd80512

Add cache comment

4824560

kinyoklion commented Mar 13, 2026

View reviewed changes

Ensure streaming is off when setStreaming(false)

304e5f3

kinyoklion commented Mar 13, 2026

View reviewed changes

cursor bot reviewed Mar 13, 2026

View reviewed changes

kinyoklion and others added 13 commits March 17, 2026 08:55

Fix mode switching.

0a03954

contract test changes - wip

0d1b333

Additional handling.

88ab6a4

Merge remote-tracking branch 'origin/mk/NOTICKET/testing-fdv2' into m…

70bdf7d

…k/NOTICKET/testing-fdv2

Connect withReasons.

04d2644

Allow mode customization. Connect withReasons.

6c1996d

Trim failing tests.

266104a

More testing, add data source updates sink.

a542dc1

No basis.

5759cef

Merge origin/main into mk/NOTICKET/testing-fdv2

79fe48c

Lint fix.

685aa67

Second example for FDv2.

0b44efd

Mock fix.

57525f3

kinyoklion closed this Mar 27, 2026

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