What is LLD and hld in frontend?

In frontend development, High-Level Design (HLD) and Low-Level Design (LLD) refer to different stages of designing a user-facing system. While these terms are more common in backend and system architecture, they apply to frontend development as well, especially when building complex web or mobile applications.

1. High-Level Design (HLD) in Frontend

HLD refers to the overall architecture and structure of the frontend application. It's a broad overview of how the different components and systems interact with each other. In the context of frontend development, HLD involves decisions about the layout, user experience (UX), and interaction between the frontend and backend.

Key Aspects of HLD in Frontend:

• Application Architecture: Defines whether the frontend will be built as a Single-Page Application (SPA), Multi-Page Application (MPA), or using frameworks like React, Angular, or Vue.
• Component Structure: Lays out how the UI will be broken into components. For example, in React, HLD would involve identifying the major components (e.g., navigation bar, sidebar, content area).
• Routing: Defines how different pages or views will be structured and how users navigate between them (e.g., client-side routing with React Router).
• State Management: Decides on the global state management strategy, such as using Redux, MobX, or the Context API.
• API Integration: High-level plan for how the frontend will interact with the backend via REST APIs or GraphQL.

Example of HLD:

For a shopping cart application, HLD might define:

• The app will be a SPA built with React.
• There will be major components like Product List, Cart, and Checkout.
• API requests will be handled through Axios to fetch product data.
• Redux will be used for global state management, handling the cart and user sessions.

2. Low-Level Design (LLD) in Frontend

LLD focuses on the detailed implementation of the components and functionality defined in the HLD. It involves the actual coding, component logic, and interaction details. LLD in frontend design deals with how specific elements will be structured, styled, and how they will function on a granular level.

Key Aspects of LLD in Frontend:

• Component Implementation: The detailed design of individual UI components, such as buttons, forms, modals, etc., with their event handling and state management.
• Styling and Layout: Specific choices for styling, like using CSS, SASS, or styled-components, and the layout strategy (e.g., Flexbox, Grid, Bootstrap).
• User Interactions: Handling user events like clicks, form submissions, and validation. For example, how a search form works, what happens on form submission, and how errors are handled.
• Data Flow: Implementation of how data flows within a component or between components. This could involve props, state management, or API calls.
• Error Handling: How UI errors are displayed (e.g., showing toast notifications, validation errors in forms).

Example of LLD:

For the shopping cart application, LLD might define:

• How the Add to Cart button component is implemented in React, including the logic to add an item to the cart, update the total, and handle out-of-stock conditions.
• CSS Grid is used to create a responsive layout for displaying products.
• Local state manages the form fields, while Redux handles the cart state globally.
• Error handling shows a modal if there’s an issue fetching product data from the API.

Differences Between HLD and LLD in Frontend

| Aspect | High-Level Design (HLD) | Low-Level Design (LLD) | |