getting-started

name	getting-started
description	Feature flags for NestJS API applications backed by OpenFeature and Go Feature Flag. Use when defining, evaluating feature flags.

Define Flags

import { createFlag } from '@wisemen/nestjs-feature-flags'

export const SearchCollectionsFlag = createFlag({
  type: 'boolean',
  defaultValue: true,
  name: 'global_search'
})

import { createFlag } from '@wisemen/nestjs-feature-flags'
import { MailProvider } from '#src/modules/mail/enums/mail-provider.enum.js'

export const MailProviderFlag = createFlag({
  type: 'string',
  enum: MailProvider,
  defaultValue: MailProvider.SCALEWAY,
  name: 'mail_provider'
})

Export flags from files matched by flagsGlob. By convention use *.flag.ts filenames so they are easy to discover.

Evaluate Flags In Application Code

After the middleware sets the context, inject FeatureFlags and call get(...) directly.

import { ConfigService } from '@nestjs/config'
import { FeatureFlags } from '@wisemen/nestjs-feature-flags'
import { MailProvider } from '#src/modules/mail/enums/mail-provider.enum.js'
import { MailProviderFlag } from './mail-provider.flag.js'

export async function mailClientFactory(
  cfg: ConfigService,
  flags: FeatureFlags
): Promise<MailClient> {
  const provider = await flags.get(MailProviderFlag)

  switch (provider) {
    case MailProvider.SCALEWAY:
      return new ScalewayMailClient(cfg)
    case MailProvider.SEND_GRID:
      return new SendGridMailClient(cfg)
    default:
      exhaustiveCheck(provider)
  }
}

Guard Controllers

import { Controller, Get } from '@nestjs/common'
import { RequireFlag } from '@wisemen/nestjs-feature-flags'
import { SearchCollectionsFlag } from './search-collections.flag.js'

@Controller('search-collections')
export class SearchCollectionsController {
  @Get()
  @RequireFlag(SearchCollectionsFlag)
  async index(): Promise<void> {}
}

RequireFlag(...) only accepts boolean flags.

Stub Flags In Tests

Create one stub from the Nest app container and expose it through your test setup so each test can override only the flags it cares about.

setup.flags.mockFlag(SearchCollectionsFlag, true)
setup.flags.mockFlag(MailProviderFlag, MailProvider.SEND_GRID)

Set Request Context In Middleware

Set the feature-flag transaction context once in auth middleware, then evaluate flags later without passing a context object around.

import { Injectable, type NestMiddleware } from '@nestjs/common'
import type { FastifyReply, FastifyRequest } from 'fastify'
import { FeatureFlagContext } from '@wisemen/nestjs-feature-flags'
import { AuthorizationResolver } from '#src/modules/auth/services/authorization-resolver.js'
import { AuthContext } from '#src/modules/auth/auth.context.js'

@Injectable()
export class AuthMiddleware implements NestMiddleware {
  constructor(
    private authContext: AuthContext,
    private flagContext: FeatureFlagContext,
    private authResolver: AuthorizationResolver
  ) {}

  async use(req: FastifyRequest, _res: FastifyReply, next: () => void): Promise<void> {
    const auth = await this.authResolver.fromAuthorization(req.headers.authorization)
    const cb = () => this.flagContext.run({ userUuid: auth.userUuid }, next)

    this.authContext.runWithAuthorization(auth, cb)
  }
}