document beforeSendMetric

Author: chargome

platform-includes/metrics/options/javascript.mdx

@@ -1,5 +1,35 @@
 The Sentry JavaScript SDK provides several options to configure how metrics are captured and sent to Sentry.
 
+### Filtering and Modifying Metrics
+
+Use the `beforeSendMetric` callback to filter or modify metrics before they're sent to Sentry. This is useful for:
+
+- Removing sensitive data from metric attributes
+- Dropping metrics you don't want to send
+- Adding or modifying attributes
+
+The callback receives a metric object and must return either a modified metric or `null` to drop it.
+
+```javascript
+Sentry.init({
+  // ...
+  beforeSendMetric: (metric) => {
+    // Drop metrics with specific attributes
+    if (metric.attributes?.dropMe === true) {
+      return null;
+    }
+
+    // Modify metric attributes
+    metric.tags = {
+      ...metric.tags,
+      processed: true,
+    };
+
+    return metric;
+  },
+});
+```
+
 ### Disabling Metrics
 
 If you want to disable metrics collection entirely, you can do so by disabling the `_experimental.enableMetrics` flag: