chore: add changelog entry for multiple metric readers support

Author: nidhiisinghh

experimental/CHANGELOG.md

@@ -10,6 +10,18 @@ For notes on migrating to 2.x / 0.200.x see [the upgrade guide](doc/upgrade-to-2
 
 ### :rocket: Features
 
+* feat(sdk-node): Add support for multiple metric readers via the new `metricReaders` option in NodeSDK configuration. Users can now register multiple metric readers (e.g., Console, Prometheus) directly through the NodeSDK constructor. The old `metricReader` (singular) option is now deprecated and will show a warning if used, but remains supported for backward compatibility. Comprehensive tests and documentation have been added. [#5760](https://github.com/open-telemetry/opentelemetry-js/issues/5760)
+  * **Migration:**
+    - Before:
+      ```js
+      const sdk = new NodeSDK({ metricReader: myMetricReader });
+      ```
+    - After:
+      ```js
+      const sdk = new NodeSDK({ metricReaders: [myMetricReader] });
+      ```
+  * Users should migrate to the new `metricReaders` array option for future compatibility. The old option will continue to work but is deprecated.
+
 ### :bug: Bug Fixes
 
 ### :books: Documentation
@@ -123,7 +135,7 @@ For notes on migrating to 2.x / 0.200.x see [the upgrade guide](doc/upgrade-to-2
 
 ### :house: (Internal)
 
-* chore(instrumentation-grpc): remove unused findIndex() function [#5372](https://github.com/open-telemetry/opentelemetry-js/pull/5372) @cjihrig
+* refactor(instrumentation-grpc): remove unused findIndex() function [#5372](https://github.com/open-telemetry/opentelemetry-js/pull/5372) @cjihrig
 * refactor(otlp-exporter-base): remove unnecessary isNaN() checks [#5374](https://github.com/open-telemetry/opentelemetry-js/pull/5374) @cjihrig
 * refactor(exporter-prometheus): remove unnecessary isNaN() check [#5377](https://github.com/open-telemetry/opentelemetry-js/pull/5377) @cjihrig
 * refactor(sdk-node): move code to auto-instantiate propagators into utils [#5355](https://github.com/open-telemetry/opentelemetry-js/pull/5355) @pichlermarc

test-backward-compatibility.js

@@ -0,0 +1,43 @@
+'use strict';
+
+const opentelemetry = require('@opentelemetry/sdk-node');
+const { metrics } = require('@opentelemetry/api');
+const { ConsoleSpanExporter } = require('@opentelemetry/sdk-trace-base');
+const { resourceFromAttributes } = require('@opentelemetry/resources');
+const { ATTR_SERVICE_NAME } = require('@opentelemetry/semantic-conventions');
+const { 
+  ConsoleMetricExporter, 
+  PeriodicExportingMetricReader 
+} = require('@opentelemetry/sdk-metrics');
+
+// Test backward compatibility with the old metricReader option
+const oldMetricReader = new PeriodicExportingMetricReader({
+  exporter: new ConsoleMetricExporter(),
+  exportIntervalMillis: 1000,
+  exportTimeoutMillis: 500,
+});
+
+const sdk = new opentelemetry.NodeSDK({
+  resource: resourceFromAttributes({
+    [ATTR_SERVICE_NAME]: 'backward-compatibility-test',
+  }),
+  traceExporter: new ConsoleSpanExporter(),
+  // This should still work but show a deprecation warning
+  metricReader: oldMetricReader,
+});
+
+console.log('Testing backward compatibility with metricReader option...');
+sdk.start();
+
+// Create a simple metric to verify it works
+const meter = metrics.getMeter('test-meter');
+const counter = meter.createCounter('test_counter');
+counter.add(1);
+
+console.log('Backward compatibility test completed successfully!');
+console.log('You should see a deprecation warning above.');
+
+sdk.shutdown().then(() => {
+  console.log('Test completed.');
+  process.exit(0);
+});