feature flagging.md

feature flagging.md

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launch darkly with tauri app?.md

launch darkly with tauri app?

Integrating LaunchDarkly with a Tauri app can be done through two approaches: using the JavaScript SDK in the frontend (webview) or the Rust SDK in the backend. Here's how to implement each:

JavaScript SDK (Frontend Approach)

This is typically the recommended approach for desktop applications since the JavaScript client-side SDK is designed for single-user contexts.¹

Installation:

npm install launchdarkly-js-client-sdk

Initialization in your frontend code:

import LDClient from 'launchdarkly-js-client-sdk';

const client = LDClient.initialize('YOUR_CLIENT_SIDE_ID', {
  key: 'user-unique-key'  // unique identifier for the user
});

// Wait for initialization
await client.waitForInitialization(5);

// Get flag values
const flagValue = client.variation('your-flag-key', false);

The SDK supports ES modules, CommonJS, and UMD formats, and can be bundled with tools like Webpack.²

Rust SDK (Backend Approach)

If you need to evaluate flags in your Tauri Rust backend, you can use the server-side Rust SDK:³⁴

Add to Cargo.toml:

cargo add launchdarkly-server-sdk

Initialize in Rust:

use launchdarkly_server_sdk::{Client, ConfigBuilder, ContextBuilder};

// Note: Uses SDK key (not client-side ID)
let config = ConfigBuilder::new("YOUR_SDK_KEY").build();
let client = Client::build(config).expect("Failed to create client");
client.start_with_default_executor();

The Rust SDK is primarily designed for multi-user systems like web servers, so for desktop apps, the JavaScript SDK is often more suitable.⁴

Recommendations for Tauri

Aspect	JavaScript SDK	Rust SDK
Location	Frontend (webview)	Backend (Rust)
Key Type	Client-side ID	SDK key 3
Best For	UI feature toggles	Backend logic flags
User Model	Single-user context	Multi-user context

For most Tauri desktop apps, using the JavaScript SDK in the frontend is simpler since your UI logic typically lives there. If you need flag evaluation in Rust commands, you can either pass flag values from the frontend via Tauri's invoke system, or initialize the Rust SDK in your backend. ^{56789101112131415}

⁂

---

but we can add this after launching right?

Yes, absolutely! You can initialize LaunchDarkly at any point after your Tauri app has launched — it doesn't need to be set up at startup.¹⁶¹⁷

Lazy Initialization

The SDK only begins connecting to LaunchDarkly when you explicitly call initialize(), so you can defer this until you actually need feature flags:¹⁷

// Initialize whenever you're ready (e.g., after user login, on a specific screen, etc.)
const client = LDClient.initialize('client-side-id-123abc', context);

// Wait for it to be ready before using flags
client.on('ready', () => {
  const flagValue = client.variation('my-flag', false);
});

Handling the Waiting Period

Before initialization completes, flag evaluations return fallback values you define, so your app won't break:¹⁸¹⁹

// This returns `false` (fallback) until SDK is initialized
const value = client.variation('my-flag', false);

You can also use waitForInitialization() with a timeout:²⁰

try {
  await client.waitForInitialization(5); // 5 second timeout
  // SDK ready, proceed with flags
} catch(err) {
  // Timed out - fallback values still work
}

Practical Tips

• Local storage caching: After the first successful initialization, the JavaScript SDK stores flag values in local storage, making subsequent startups faster²¹
• Network resilience: If the SDK loses connection, flags still work using cached/stored state — no network needed for evaluation¹⁹
• Single instance: Initialize once and reuse the same client instance throughout your app's lifetime²²

So you have full flexibility to add LaunchDarkly whenever it makes sense in your app flow — after login, on first feature flag need, or on a specific user action. ^{2324252627282930}

⁂

---

also posthog seem to support feature flagging. we want to use that for analytics. so might use that for launch flag as well?

Yes, that's a great idea! Using PostHog for both analytics and feature flags simplifies your stack significantly. PostHog offers full feature flag functionality comparable to LaunchDarkly, and you get the benefit of one SDK for everything.³¹³²

PostHog Feature Flags in Tauri

The JavaScript SDK handles both analytics and feature flags:³³

import posthog from 'posthog-js';

// Initialize once - handles both analytics and flags
posthog.init('YOUR_PROJECT_API_KEY', {
  api_host: 'https://app.posthog.com'
});

// Check feature flags
const isEnabled = posthog.isFeatureEnabled('my-feature');

// Multivariate flags (A/B/C variants)
const variant = posthog.getFeatureFlag('my-experiment');

Handling Flag Loading

Flags are fetched in the background when the app opens and cached in storage. For the first visit, you can listen for when flags are ready:³⁴

posthog.onFeatureFlags((flags) => {
  // Flags are now available
  if (posthog.isFeatureEnabled('new-ui')) {
    // Show new UI
  }
});

PostHog vs LaunchDarkly

Aspect	PostHog	LaunchDarkly
Pricing	Free tier with generous limits, open-source 32	Paid, enterprise-focused
Feature flags	Full support (boolean + multivariate) 31	Full support
Analytics	Built-in (events, sessions, funnels)	Requires integration
Experiments	Included with analytics tie-in 35	Included
SDKs	Client, mobile, and server-side by default 35	Server-side by default

Tauri-Specific Integration

There's even a dedicated Tauri plugin for PostHog if you want backend integration:³⁶

# Cargo.toml
[dependencies]
tauri-plugin-better-posthog = "..."

Using PostHog for both analytics and feature flags means:

• One SDK to initialize and maintain
• Automatic correlation between flag exposures and user behavior
• Built-in experiment analysis — no need to export data elsewhere³¹

This is a solid choice for your Tauri app! ^{373839404142434445}

⁂

Footnotes

1. https://launchdarkly.com/docs/sdk/client-side/javascript ↩

2. https://devhunt.org/blog/launchdarkly-javascript-sdk-simplifies-feature-flags ↩

3. https://launchdarkly.com/docs/sdk/server-side/rust ↩ ↩²

4. https://github.com/launchdarkly/rust-server-sdk ↩ ↩²

5. https://v2.tauri.app/develop/configuration-files/ ↩

6. https://v2.tauri.app/start/prerequisites/ ↩

7. https://docs.rs/launchdarkly-server-sdk ↩

8. https://docs.sentry.io/platforms/javascript/configuration/integrations/launchdarkly/ ↩

9. https://github.com/tauri-apps/tauri/issues/11790 ↩

10. https://launchdarkly.com/docs/sdk/server-side/rust/implementation-v1 ↩

11. https://launchdarkly.com/integrations/ ↩

12. https://github.com/tauri-apps/tauri/issues/4915 ↩

13. https://www.reddit.com/r/vuejs/comments/jnzfem/integrating_launch_darkly_with_vuejs/ ↩

14. https://dev.to/rain9/tauri-6-invoke-desktop-application-functionality-through-the-browser-811 ↩

15. https://launchdarkly.com/docs/guides/integrations/using-integrations ↩

16. https://launchdarkly.com/blog/5-best-practices-for-getting-started-with-launchdarkly/ ↩

17. https://launchdarkly.com/docs/sdk/client-side/javascript ↩ ↩²

18. https://launchdarkly.com/docs/sdk/concepts/getting-started ↩

19. https://launchdarkly.com/docs/home/getting-started/setting-up ↩ ↩²

20. https://launchdarkly.com/docs/sdk/features/config ↩

21. https://launchdarkly.com/docs/sdk/features/bootstrapping ↩

22. https://launchdarkly.github.io/lua-server-sdk/modules/launchdarkly-server-sdk.html ↩

23. https://github.com/launchdarkly/node-server-sdk/issues/289 ↩

24. https://support.launchdarkly.com/hc/en-us/articles/23582566247579-Error-LaunchDarkly-SDK-already-initialized-React-Native-SDK ↩

25. https://blog.arcjet.com/node-js-security-dynamic-rate-limiting-with-arcjet-and-launchdarkly/ ↩

26. https://stackoverflow.com/questions/75086682/using-launch-darkly-3-0-1-i-am-getting-error-while-initializing-the-app ↩

27. https://launchdarkly.com/docs/sdk/observability/javascript ↩

28. https://dev.to/lazypro/unleash-vs-launchdarkly-25e3 ↩

29. https://launchdarkly.com/docs/sdk/concepts/data-stores ↩

30. https://launchdarkly.com/docs/sdk/features/storing-data ↩

31. https://posthog.com/blog/posthog-vs-launchdarkly ↩ ↩² ↩³

32. https://posthog.com/blog/best-launchdarkly-alternatives ↩ ↩²

33. https://posthog.com/docs/references/posthog-js ↩

34. https://posthog.com/docs/feature-flags/adding-feature-flag-code ↩

35. https://posthog.com/docs/migrate/launchdarkly ↩ ↩²

36. https://lib.rs/crates/tauri-plugin-better-posthog ↩

37. https://v1.tauri.app ↩

38. https://vercel.com/templates/edge-middleware/posthog-with-flags-sdk-and-next-js ↩

39. https://flags-sdk.dev/providers/posthog ↩

40. https://isabell.hashnode.dev/convert-your-web-project-to-a-desktop-app-with-tauri ↩

41. https://posthog.com/docs/feature-flags/creating-feature-flags ↩

42. https://www.statsig.com/perspectives/feature-flags-experimentation-pricing-comparison ↩

43. https://posthog.com/docs/feature-flags ↩

44. https://posthog.com/docs/libraries/js/usage ↩

45. https://posthog.com/docs/feature-flags/installation ↩