chore: Add docs for emitted events. (#273)

packages/sdk/server-node/src/api/LDClient.ts

@@ -11,6 +11,11 @@ import { BigSegmentStoreStatusProvider } from './interfaces';
  * and continue to use it throughout the lifetime of the application, rather than creating instances
  * on the fly.
  *
+ * Note that `LDClient` inherits from `EventEmitter`, so you can use the standard `on()`, `once()`, and
+ * `off()` methods to receive events. The standard `EventEmitter` methods are not documented here; see the
+ * {@link https://nodejs.org/api/events.html#events_class_eventemitter|Node API documentation}. For a
+ * description of events you can listen for, see {@link on}.
+ *
  */
 export interface LDClient extends LDClientCommon, EventEmitter {
   /**
@@ -21,4 +26,30 @@ export interface LDClient extends LDClientCommon, EventEmitter {
    * {@link interfaces.BigSegmentStoreStatusProvider} for more about this functionality.
    */
   readonly bigSegmentStoreStatusProvider: BigSegmentStoreStatusProvider;
+
+  /**
+   *
+   * Registers an event listener that will be called when the client triggers some type of event.
+   *
+   * This is the standard `on` method inherited from Node's `EventEmitter`; see the
+   * {@link https://nodejs.org/api/events.html#events_class_eventemitter|Node API docs} for more
+   * details on how to manage event listeners. Here is a description of the event types defined
+   * by `LDClient`.
+   *
+   * - `"ready"`: Sent only once, when the client has successfully connected to LaunchDarkly.
+   * Alternately, you can detect this with [[waitForInitialization]].
+   * - `"failed"`: Sent only once, if the client has permanently failed to connect to LaunchDarkly.
+   * Alternately, you can detect this with [[waitForInitialization]].
+   * - `"error"`: Contains an error object describing some abnormal condition that the client has detected
+   * (such as a network error).
+   * - `"update"`: The client has received a change to a feature flag. The event parameter is an object
+   * containing a single property, `key`, the flag key. Note that this does not necessarily mean the flag's
+   * value has changed for any particular context, only that some part of the flag configuration was changed.
+   * - `"update:KEY"`: The client has received a change to the feature flag whose key is KEY. This is the
+   * same as `"update"` but allows you to listen for a specific flag.
+   *
+   * @param event the name of the event to listen for
+   * @param listener the function to call when the event happens
+   */
+  on(event: string | symbol, listener: (...args: any[]) => void): this;
 }