Launchdarkly Metric Instrument

# SDK Track Patterns

How to call `track()` in each LaunchDarkly SDK. Use this reference to match the patterns already in use in the codebase — and to add the right call when starting fresh.

The key distinction across all SDKs: **server-side SDKs require a context per call; client-side SDKs do not.**

---

## JavaScript / TypeScript — Node.js (Server-side)

**Package:** `@launchdarkly/node-server-sdk` (v9+) or `launchdarkly-node-server-sdk` (v6–v8)

```bash
npm install @launchdarkly/node-server-sdk
```

```typescript
import * as ld from '@launchdarkly/node-server-sdk';

const client = ld.init(process.env.LD_SDK_KEY!);
await client.waitForInitialization();

// Count / occurrence metric (no metricValue)
client.track('checkout-completed', context);

// Value metric — pass the measurement as metricValue
client.track('api-response-time', context, null, responseTimeMs);

// With custom data payload
client.track('item-purchased', context, { itemId: 'abc123', category: 'apparel' }, purchaseAmount);

// Flush explicitly in tests / short-lived processes
await client.flush();
```

---

## JavaScript / TypeScript — Browser (Client-side)

**Package:** `launchdarkly-js-client-sdk`

```bash
npm install launchdarkly-js-client-sdk
```

```typescript
import * as ld from 'launchdarkly-js-client-sdk';

const client = ld.initialize(clientSideId, context);
await client.waitForInitialization();

// Count / occurrence metric — no context, no metricValue
client.track('signup-completed');

// Value metric
client.track('page-load-time', null, performanceMs);

// With custom data
client.track('item-added-to-cart', { itemId: 'abc123' }, itemPrice);

// Flush (useful in tests or before navigating away)
await client.flush();
```

---

## React (Client-side)

**Package:** `launchdarkly-react-client-sdk`

```bash
npm install launchdarkly-react-client-sdk
```

```tsx
import { useLDClient } from 'launchdarkly-react-client-sdk';

function CheckoutButton() {
  const ldClient = useLDClient();

  const handleSubmit = async () => {
    await processCheckout();

    // Count / occurrence metric
    ldClient?.track('checkout-completed');

    // Value metric
    ldClient?.track('checkout-revenue', null, orderTotal);
  };

  return <button onClick={handleSubmit}>Complete Order</button>;
}
```

**Initialization** (typically in the app root via `LDProvider` or `asyncWithLDProvider`):

```tsx
import { LDProvider } from 'launchdarkly-react-client-sdk';

// Wrap your app — context is set here, not in each track() call
<LDProvider clientSideID={clientSideId} context={userContext}>
  <App />
</LDProvider>
```

---

## Python (Server-side)

**Package:** `launchdarkly-server-sdk`

```bash
pip install launchdarkly-server-sdk
```

```python
import ldclient
from ldclient.config import Config

ldclient.set_config(Config(sdk_key))
client = ldclient.get()

# Count / occurrence metric
client.track('checkout-completed', context)

# Value metric
client.track('api-response-time', context, None, response_time_ms)

# With data payload
client.track('item-purchased', context, {'item_id': 'abc123'}, purchase_amount)

# Flush
client.flush()
```

---

## Go (Server-side)

**Package:** `github.com/launchdarkly/go-server-sdk/v7`

```bash
go get github.com/launchdarkly/go-server-sdk/v7
```

```go
import (
    ld "github.com/launchdarkly/go-server-sdk/v7"
    "github.com/launchdarkly/go-server-sdk/v7/ldcontext"
)

client, _ := ld.MakeClient(sdkKey, 5*time.Second)
defer client.Close()

// Count / occurrence metric
client.TrackEvent("checkout-completed", context)

// Value metric
client.TrackMetric("api-response-time", context, responseTimeMs, nil)

// With data payload
data := ldvalue.BuildObject().Set("itemId", ldvalue.String("abc123")).Build()
client.TrackData("item-purchased", context, data)
```

---

## Java (Server-side)

**Package:** `com.launchdarkly:launchdarkly-java-server-sdk`

```xml
<!-- Maven -->
<dependency>
  <groupId>com.launchdarkly</groupId>
  <artifactId>launchdarkly-java-server-