> ## Documentation Index
> Fetch the complete documentation index at: https://docs.westyx.cloud/llms.txt
> Use this file to discover all available pages before exploring further.

# Node.js SDK - Configuration

> NexusConfig field reference and TTL guidance for the Node.js SDK.

`NexusConfig` is a plain TypeScript interface holding every value required to construct a client. Pass it to `NexusClient.create()`.

```ts theme={null}
const client = await NexusClient.create({
  endpoint: 'https://<slug>.westyx.dev', // required
  apiKey:   'wxs_...',               // required
  ttl:      60_000,                      // optional, default 60 000 ms
});
```

## Field reference

| Field                  | Type                 | Default     | Description                                                                                                                                                                                                  |
| ---------------------- | -------------------- | ----------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ |
| `endpoint`             | `string`             | -           | Full service URL, e.g. `https://<slug>.westyx.dev`. The slug embedded in the host is also used as the `Host` header on every request (Double-Gate requirement).                                              |
| `apiKey`               | `string?`            | `undefined` | Raw `wxs_...` or `wxp_...` key. Sent verbatim in `X-Nexus-API-Key`. Optional when `wif.enabled = true`.                                                                                                      |
| `ttl`                  | `number`             | `60_000`    | Local cache TTL in **milliseconds**. After this elapses, the next read triggers a one-shot background refresh while still serving the stale cache.                                                           |
| `wif`                  | `WIFConfig?`         | `undefined` | *(v0.2.0)* Workload Identity Federation. When `enabled: true`, the SDK exchanges an OIDC token for a session JWT and uses bearer auth instead of the API key. See [Workload identity](workload-identity).    |
| `streamObserver`       | `StreamObserver?`    | `undefined` | *(v0.2.0)* Optional structured-callback observer for SSE lifecycle events. See [Stream observer](stream-observer).                                                                                           |
| `sseReconnectCooldown` | `number \| number[]` | `undefined` | Schedule for reconnecting SSE after falling back to TTL polling. Unit: **minutes**. `undefined` = default `[5, 10, 20, 40, 60]` min. Number = fixed interval. Array = custom schedule (stays at last value). |

<Note>
  Other Westyx Nexus SDKs (Spring Boot, Python, Go, .NET) call this field `baseUrl` / `BaseUrl` / `base_url`. The Node.js SDK uses `endpoint` to match the original SDK contract; both names mean the same thing.
</Note>

## API key types

| Prefix    | Access                                                            | Sync response shape                                      |
| --------- | ----------------------------------------------------------------- | -------------------------------------------------------- |
| `wxs_...` | Full - all configs, all secrets, all flags                        | `configs`, `secrets`, and `flags` populated              |
| `wxp_...` | Restricted - only public configs and flags (filtered server-side) | `secrets` field is **entirely absent** from the response |

<Warning>
  Calling `getSecret(...)` with a public key throws `NexusPublicKeyError` synchronously, before the network call.
</Warning>

## Where to keep the API key

Standard Node.js practice - environment variables:

```ts theme={null}
const client = await NexusClient.create({
  endpoint: process.env.NEXUS_URL!,
  apiKey:   process.env.NEXUS_API_KEY!,
});
```

For more structured config, libraries like `dotenv`, `convict`, or `zod` work seamlessly:

```ts theme={null}
import { z } from 'zod';

const env = z.object({
  NEXUS_URL:     z.string().url(),
  NEXUS_API_KEY: z.string().regex(/^(wxs|wxp)_/),
}).parse(process.env);

const client = await NexusClient.create({
  endpoint: env.NEXUS_URL,
  apiKey:   env.NEXUS_API_KEY,
});
```

The SDK itself never logs the raw key.

## Choosing the TTL

The TTL is a tradeoff between staleness window and redundant network traffic. With SSE enabled (the default), **changes propagate in milliseconds regardless of the TTL** - the TTL only matters as a safety net if the stream falls back.

| Use case                                     | Suggested `ttl`      |
| -------------------------------------------- | -------------------- |
| Frequently-changing flags, latency-sensitive | `30_000` (30 s)      |
| Standard configs with SSE                    | `60_000` (default)   |
| Stable production secrets                    | `300_000` (5 min)    |
| Boot-time only, never rechecked              | `3_600_000` (1 hour) |

<Info>
  When SSE is connected, the SDK clamps the effective TTL to **at least 60 s** - there's no point polling more aggressively when the stream pushes events the moment they happen.
</Info>