Choose who gets it.
See who uses it.

import { createFlagClient } from "@vlag/sdk";

const flags = createFlagClient({
  apiUrl: process.env.VLAG_API_URL!,
  apiKey: process.env.VLAG_API_KEY!,
  environment: "production",
  defaults: { "new-checkout": false },
});

const context = { userId: currentUser.id, attributes: { plan: currentUser.plan } };
const result = await flags.getBoolean(
  "new-checkout",
  context,
  false,
);

if (result.value) {
  showNewCheckout();
  flags.trackExposure("new-checkout", context, result); // when the feature is shown
}

// Wire into the app's successful-checkout callback:
const recordCheckoutUse = () =>
  flags.trackUsage("new-checkout", context, result);

// After tracking in a Worker request: ctx.waitUntil(flags.flush())

# Replace both placeholders with this user's stable ID and actual account plan.
# In Bash, pipefail keeps a failed curl request from appearing successful through jq.
# To measure exposure/use, also POST feature_exposed/feature_used events to /v1/events.
set -o pipefail
curl --fail-with-body --silent --show-error \
  "$VLAG_API_URL/v1/evaluate" \
  -H "Authorization: Bearer $VLAG_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{"flags":[{"key":"new-checkout","fallback":false}],"environment":"production","context":{"userId":"REPLACE_WITH_STABLE_USER_ID","attributes":{"plan":"REPLACE_WITH_USER_PLAN"}}}' \
  | jq '.data.results[0].value'