Feature Flags Web Components

StencilJS-powered web components for feature-flag previews, bundled with tsdown and shipped as ESM-only via Bun.

Setup

bun install
# scripts
bun run dev    # watch build
bun run build  # stencil build + tsdown bundle
bun run lint   # biome
bun run test   # vitest

Using the modal

import { registerFeatureFlagComponents } from '@example/feature-flags-wc';

await registerFeatureFlagComponents();

<feature-flag-preview-modal
  id="feature-preview-modal"
  open
  api-endpoint="https://flags.basestack.co/api/v1/flags/preview"
  project-key="YOUR_PROJECT_KEY"
  storage-key="bs-flags-preview-state"
  heading="Feature preview dialog"
  subtitle="Select and enable previews tailored to your workflow."
  selection-prompt="Select a preview to inspect"
  selection-placeholder="Choose a feature on the left to preview its details."
  enable-label="Enable"
  enabled-label="Enabled"
  loading-label="Loading feature previews…"
  empty-label="No feature flags are available right now."
></feature-flag-preview-modal>

<script>
  const modal = document.getElementById("feature-preview-modal");
  if (modal) {
    modal.metadata = {
      user: { id: "usr_123" },
      payment: { plan: "pro" },
    };
  }
</script>

• When api-endpoint is omitted, the component uses https://flags.basestack.co/api/v1/flags/preview.
• Provide either project-key (header x-project-key) or environment-key (header x-environment-key) for the Basestack API. If neither is provided, built-in mock flags are shown.
• The component sends a POST request to the preview endpoint and supports optional metadata in the request JSON body.
• User choices are persisted to localStorage under storage-key.
• All user-facing labels (heading, subtitle, prompts, button text, badges, empty/loading states) are optional attributes so you can localize or reword them per embed.
• The SDK helpers exported from src/sdk give you headless access to fetching and storage logic.

Feedback modal

<feature-flag-feedback-modal
  open
  flag-key="command-palette"
  feature-name="Command palette"
  project-key="YOUR_PROJECT_KEY"
  environment-key="YOUR_ENVIRONMENT_KEY"
  heading="Feedback"
  mood-prompt="How did this feature make you feel?"
  rating-prompt="How would you rate the quality of this feature?"
  feedback-label="Your feedback"
  feedback-placeholder="Anything you'd like to add? Your input is valuable to us"
  submit-label="Send Feedback"
></feature-flag-feedback-modal>

• Feedback is sent to https://flags-api.basestack.co/v1/flags/feedback/:flagKey with the appropriate x-project-key or x-environment-key header.

Architecture

This package has a dual-build architecture using two separate tools:

Stencil (Web Components)

Stencil compiles the web components (<feature-flag-preview-modal>, <feature-flag-feedback-modal>) into framework-agnostic custom elements.

• Output: dist/components/
• Usage: Components are self-contained and can be used directly without the SDK

// Direct component usage (no SDK)
import { defineCustomElement } from '@basestack/flags-wc/components/feature-flag-preview-modal';

defineCustomElement();

tsdown (SDK Bundle)

tsdown bundles the SDK layer — a lightweight wrapper that provides:

• Re-exported utilities and TypeScript types

• Output: dist/sdk/

• Entry: src/sdk/index.ts

// SDK usage (recommended)
import { registerFeatureFlagComponents, FeatureFlagClient } from '@basestack/flags-wc';

await registerFeatureFlagComponents();

Why two build tools?

Tool	Purpose	Output
Stencil	Compiles .tsx components into native Web Components with Shadow DOM, scoped styles, and lazy-loading	dist/components/
tsdown	Bundles the SDK entry point with tree-shaking, minification, and TypeScript declarations	dist/sdk/

The components don't depend on the SDK — the SDK depends on the components. This means you can use the raw Stencil components directly if you prefer, or use the SDK for a more ergonomic developer experience.