What is Single-SPA?

A Single-SPA (single-spa) application is a micro-frontend framework that enables you to build and manage multiple independent micro-frontend applications within a single frontend. It lets you work with multiple frameworks (such as Angular, React, Vue) in one application, allowing each micro-frontend to operate independently, yet function cohesively as a unified app.

Key Features of Single-SPA

Framework Agnostic: You can use Angular, React, Vue, or any other framework, or even multiple frameworks, in a single application.
Independent Deployment: Each micro-frontend can be independently deployed and updated without impacting the others.
Improved Scalability and Maintainability: Since each application or module is isolated, managing and scaling applications is easier.
Performance Optimization: Single-SPA loads applications only when they’re needed, optimizing resources.

How Single-SPA Works

Root Config: Single-SPA has a root configuration that registers each micro-frontend application and determines when each should be loaded based on route matching.
Applications and Parcels: Applications are complete micro-frontends, while parcels are more like independent widgets.
Lifecycle Management: Single-SPA handles the lifecycle of each micro-frontend (mounting, updating, and unmounting), making it seamless for end users.

Single-SPA is useful in complex, large-scale applications where modularity, flexible scaling, and technology independence are priorities.

Single-SPA (Single-Single Page Application) operates by coordinating multiple micro-frontend applications within a single web application. Here’s a detailed look at how it works:

1. Micro-Frontend Architecture

Each micro-frontend in Single-SPA is a standalone application built with its own framework (React, Angular, Vue, etc.), making each micro-frontend independent in terms of codebase, deployment, and lifecycle.
These applications can be loaded dynamically based on routes, so they operate only when required.

2. Root Config and Routing

The root configuration is the main application file that registers all micro-frontends and decides when to load each one.
It listens for changes in the URL and triggers each micro-frontend based on the defined routing rules.
You define conditions for when each micro-frontend should activate. For example, an Angular app might load at /dashboard, while a React app loads at /profile.

3. Lifecycle Management

Each micro-frontend has a set of lifecycle functions that Single-SPA manages, including:

Bootstrap: Initializes the application.
Mount: Loads and renders the application into the DOM.
Unmount: Removes the application from the DOM when it’s no longer needed.

These lifecycle events ensure that only one micro-frontend is active at a time based on the current route, allowing independent loading and unloading.

4. Shared State and Communication

Single-SPA provides methods for micro-frontends to communicate with each other or share a common state.
You can use libraries like Redux, RxJS, or Context API for shared state management, enabling data consistency across different micro-frontends.
This allows one micro-frontend to respond to changes in another without tightly coupling them.

5. Parcel System for Smaller Components

Single-SPA supports parcels, which are smaller independent components (like widgets or mini-applications).
Parcels are useful when you want reusable components or need to embed a piece of functionality in multiple applications within the Single-SPA environment.

6. Lazy Loading and Performance Optimization

Single-SPA loads micro-frontends only when they’re needed based on route matching, reducing the initial bundle size and enhancing load times.
This approach also enables faster updates, as only the specific micro-frontend needs redeployment without affecting the whole application.

7. Independent Deployment and Version Control

Because each micro-frontend is isolated, they can be independently updated, scaled, or deployed. This makes it easier to work with multiple teams on different parts of the same application.

Example Workflow

Imagine you have a dashboard built with Angular, and a user profile section in React. When a user navigates to /dashboard, Single-SPA loads only the Angular application. If the user navigates to /profile, Single-SPA unmounts the Angular app and mounts the React app, making transitions seamless and modular.

Summary

In short, Single-SPA leverages micro-frontend architecture to integrate different frameworks and technologies into a single cohesive user experience, improving scalability, deployment flexibility, and reducing interdependency among teams.