NestJS Guide

NestJS projects place evaluation logic inside injectable services. FlagLint scans TypeScript source directly — no Nest runtime metadata is required.

Typical directory structure

src/
  app.module.ts
  platform/
    feature-flags.module.ts       # ← OpenFeature setup lives here
    feature-flags.service.ts      # ← shared evaluation wrapper
  checkout/
    checkout.service.ts           # direct LD calls to migrate
    checkout.module.ts
  pricing/
    pricing.service.ts

Step 1 — Audit, excluding tests

npx flaglint audit ./src --exclude-tests

✓ Audit complete: 11 flags — 1 high risk, 10 medium risk

The --exclude-tests flag prevents test fixtures from inflating counts.

Step 2 — Scan for detailed inventory

npx flaglint scan ./src --exclude-tests --format json --output flag-inventory.json

Use the JSON output to cross-reference flags with your NestJS module boundaries before migrating.

Step 3 — Set up a shared OpenFeature service

Create src/platform/feature-flags.service.ts:

import { Injectable, OnModuleInit } from "@nestjs/common";
import { OpenFeature, Client } from "@openfeature/server-sdk";
import { LaunchDarklyProvider } from "@launchdarkly/openfeature-node-server";

@Injectable()
export class FeatureFlagsService implements OnModuleInit {
  client!: Client;

  async onModuleInit() {
    await OpenFeature.setProviderAndWait(
      new LaunchDarklyProvider(process.env.LD_SDK_KEY!)
    );
    this.client = OpenFeature.getClient();
  }
}

Export it from feature-flags.module.ts and import it into any module that needs flag evaluation.

Add the binding to .flaglintrc:

{
  "exclude": ["**/*.spec.ts", "**/*.test.ts"],
  "openFeatureClientBindings": [
    {
      "importName": "openFeatureClient",
      "modulePatterns": ["**/platform/feature-flags.service"]
    }
  ]
}

Step 4 — Preview migration

npx flaglint migrate ./src --dry-run --exclude-tests

Example diff inside a NestJS service:

const enabled = await this.ldClient.boolVariation("new-checkout", ctx, false);
const enabled = await this.featureFlagsService.client.getBooleanValue("new-checkout", false, ctx);

Review each diff. FlagLint will not rewrite calls where the client binding is ambiguous or injected through a dynamic reference.

Step 5 — Apply on a branch

git checkout -b migrate/openfeature
npx flaglint migrate ./src --apply --exclude-tests

Step 6 — Enforce in CI

npx flaglint validate ./src --no-direct-launchdarkly --exclude-tests

Wrapper detection

If your team uses a shared evaluation wrapper that accepts dynamic flag keys, configure it so FlagLint surfaces those calls for manual review:

{
  "wrappers": ["evaluateFlag", "getFeatureFlag"]
}

Wrappers are reported but never auto-rewritten.

Edit this page · Report an unsupported pattern · Next: Monorepos