Real-Time Processing Updates Using Server-Sent Events (SSE) with Vue.js and NestJS

Enhancing User Experience with Real-Time Processing Using SSE

In today’s digital era, modern web applications often demand real-time feedback, especially when handling long-running or background operations. This not only improves user engagement but also provides transparency into backend processes. In this article, we’ll delve into how real-time updates can be efficiently implemented using Server-Sent Events (SSE) and the EventSource API in a Vue.js frontend, working alongside a NestJS backend.

Understanding the Client’s Needs

Before jumping into the technical implementation, it’s essential to understand the problem we aimed to solve.

The client’s backend system was developed using NestJS, a framework known for its support of event-driven architectures. Their application involved heavy background processing tasks—such as converting or processing large PDF files—and they needed a reliable way to notify users of the ongoing status without using polling, which can put unnecessary load on both the server and client.

Their requirements were clear:

• Deliver live status updates from the server during processing.
• Avoid repetitive polling to reduce overhead.
• Maintain a lightweight and bandwidth-efficient solution.
• Ensure smooth state transitions in the UI, with robust error handling.

With these points in mind, SSE and the EventSource API presented themselves as an ideal choice for implementing one-way real-time communication from server to client.

Why Server-Sent Events (SSE)?

SSE provides a simple yet powerful mechanism to send updates from a server to the browser over a single HTTP connection. Unlike WebSockets, SSE is unidirectional, meaning it only allows the server to push updates to the client, making it perfect for status updates and live notifications. It also benefits from built-in support in modern browsers and straightforward implementation.

Key Features in Our Real-Time Update Module

Our custom Vue.js component designed for handling real-time updates incorporates the following core features:

Live Progress Tracking: As tasks progress on the server, updates are pushed instantly to the client using SSE.
Robust Error Handling: The component gracefully handles connection drops, server-side errors, and message formatting issues.
Smooth UI Transitions: Once a background task is complete, the UI automatically advances to the next step.
Optimized Resource Usage: Since data is only sent when changes occur, network usage is minimal. Also, the component ensures proper cleanup to prevent memory leaks.

This implementation ensures that users stay informed at every stage of the background task, without needing to manually refresh or interact with the page.

UI for Processing State

This component visually indicates processing progress while receiving real-time updates from the server.

Setting Up the EventSource Connection

An EventSource connection is established to receive real-time updates from the server, enabling the client to react to changes immediately as they happen.

When the server sends a message handler processes the incoming data. The message is parsed, and specific actions are taken based on the data content. This could involve error handling, updating the UI with progress, or triggering further actions based on the event type (e.g., workflow completion, error notifications).

Important Considerations from Our Implementation

During the development process, we ensured that several critical factors were addressed to maintain performance and reliability:

Proper Connection Cleanup: It’s essential to close the EventSource connection when it’s no longer needed to prevent memory leaks and resource waste.
Smart Reconnection Strategy: In production environments, implementing an exponential backoff mechanism for reconnecting ensures more stable and efficient handling of connection interruptions.
Secure Message Handling: All incoming messages are thoroughly validated before being processed to maintain data integrity and prevent unexpected behavior.