> For the complete documentation index, see [llms.txt](https://docs.digit.org/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.digit.org/sandbox/platform/architecture/sandbox-ui/low-level-design/root-app.md).

# Root App

## **Overview**

The Root App is a pure JavaScript application based on the Single-SPA framework. It serves as the primary orchestrator for loading and managing multiple micro frontends within a single-page application (SPA). The application uses Single-SPA's layout engine and micro frontend configuration to dynamically load and render micro frontends based on a predefined layout.

## **Components**

1. **Single-SPA Core**
   * **Purpose**: Provide the core functionalities for registering, loading, and managing micro frontends.
   * **Responsibilities**:
     * Register micro frontend applications.
     * Start the Single-SPA application orchestrator.
     * Manage lifecycle events of the micro frontends.
2. **Single-SPA Layout**
   * **Purpose**: Define the layout structure of the microfrontends.
   * **Responsibilities**:
     * Parse the layout configuration.
     * Construct routes based on the layout.
     * Activate the layout engine to manage micro frontend positioning and rendering.
3. **Micro frontends Applications**
   * **Purpose**: Individual micro frontend applications that provide specific functionalities within the root app.
   * **Responsibilities**:
     * Implement specific business logic and UI components.
     * Be dynamically loaded based on the route and layout configuration.
4. **Custom Properties**
   * **Purpose**: Provide dynamic properties to microfrontends.
   * **Responsibilities**:
     * Extract and pass the root tenant information from the URL.
     * Provide the base application URL to micro frontends.

## **Key Functions & Configuration**

1. **`getRootTenant` Function**
   * **Purpose**: Extract the root tenant from the URL.
2. **Layout Configuration**
   * **Purpose**: Define the layout structure using Single-SPA layout configuration.
3. **Micro frontend Applications**
   * **Purpose**: Define and register micro frontends based on the layout configuration.
4. **Layout Engine**
   * **Purpose**: Manage the positioning and rendering of microfrontends.
5. **Register Applications**
   * **Purpose**: Register each micro frontend application with custom properties.
6. **Start Single-SPA**
   * **Purpose**: Start the Single-SPA orchestrator.

## **Data Flow**

1. **Initialization**
   * On application start, the `getRootTenant` function extracts the root tenant from the URL.
   * The `constructRoutes` function parses the micro frontend layout configuration.
2. **Application Registration**
   * The `constructApplications` function constructs the applications based on the routes.
   * Each application is registered with custom properties, including `rootTenant` and `baseAppURL`.
3. **Layout Management**
   * The `constructLayoutEngine` function activates the layout engine to manage micro frontend positioning.
4. **Application Start**
   * The `start` function initializes the Single-SPA framework, enabling micro frontend orchestration.


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