onReconnect

OnReconnect is a term used in real-time networking and client libraries to denote a callback or event that handles the moment when a connection is being re-established after a disruption. It is commonly employed in systems that support automatic reconnection, such as WebSocket clients, messaging protocols, and live data streams. The exact behavior of onReconnect—whether it fires during a retry, after a successful reconnection, or both—depends on the specific library or framework.

Usage and context vary across implementations. Some libraries expose onReconnect as a property that the application assigns a function to, while others provide an event that can be listened to with addEventListener or a similar mechanism. Because the name and signature are not standardized, developers should consult the documentation for the particular library in use. In practice, onReconnect is often used to update UI indicators, adjust backoff strategies, or re-subscribe to topics or channels after a connection is restored.

Common patterns and signatures include supplying the attempt number, the delay before the next retry, or information about the last error. Example (pseudocode): client.onReconnect = function(attempt, delay, lastError) { log("Reconnect attempt", attempt, "in", delay); } or client.addEventListener("reconnect", handler). It is important to ensure that onReconnect handlers are efficient and idempotent, as reconnection workflows can trigger multiple times in fluctuating network conditions.

See also: onConnect, onDisconnect, reconnect strategies, backoff algorithms, WebSocket, MQTT, Socket.IO.