Eseményforrása

Eseményforrása, often referred to in English as "Event Source" or abbreviated as "ES," is a technology primarily used in web development to enable real-time data updates from a server to a client without the need for the client to poll the server repeatedly. It is defined in the HTML specification as part of the Server-Sent Events (SSE) protocol, which allows a web server to push updates to a single client over a persistent HTTP connection.

The SSE protocol operates on a simple push model, where the server sends data to the client as it becomes available, rather than the client requesting updates at fixed intervals. This approach is particularly useful for applications requiring live updates, such as stock tickers, live sports scores, chat applications, or notifications. The connection remains open as long as the client is active, ensuring minimal latency and efficient use of bandwidth.

In practice, an event source is established by the client using the `<event-source>` HTML element or the JavaScript `EventSource` interface. The server responds with a stream of data formatted as a series of messages, each prefixed with an event name, optional event ID, and data payload. Clients can subscribe to specific events or listen to all events, processing the incoming data dynamically. Error handling is also supported, allowing the client to reconnect automatically if the connection is lost.

Eseményforrása is widely supported in modern web browsers and is considered a lightweight alternative to more complex real-time communication protocols like WebSockets. Its simplicity and efficiency make it a popular choice for applications requiring one-way, server-to-client communication. However, it does not support bidirectional communication, which is a limitation in scenarios requiring two-way interaction between the client and server.