ReactJS Training in Ahmedabad

Lifecycle methods are special functions in class components that run at different phases: mounting, updating, and unmounting. Examples: componentDidMount, shouldComponentUpdate.

useEffect allows performing side effects (e.g., fetching data, timers) in functional components. It replaces lifecycle methods like componentDidMount.

useState is a React Hook that lets you add and manage state in functional components.

useRef returns a mutable object whose .current property holds a value. It can persist values between renders or reference DOM elements.

useContext lets you consume values from a React Context without using props drilling.

useMemo is used to memoize the result of an expensive function and avoid recalculating it on every render unless dependencies change.

useCallback memoizes a function and returns a cached version, useful when passing functions to child components.

The dependency array tells React when to re-run the effect. If empty, it runs once; if values are added, it runs when those values change.

A basic understanding of HTML, CSS, and JavaScript is recommended. If you’re new to programming, TOPS also offers foundational web development courses to help you get started before diving into React.

Keys are unique identifiers used in lists to help React track changes to elements efficiently. They assist in the diffing algorithm during reconciliation, enabling React to detect which elements were added, removed, or reordered. Using stable and unique keys, such as IDs, improves performance and ensures consistent component behavior during re-renders.

A controlled component is an input element whose form data is managed by the React component’s state. Any change in the input is captured through an event handler, and the new value is updated in the component’s state. This provides a single source of truth for form inputs, offering better control, validation, and predictability.

An uncontrolled component allows the browser to manage the form input’s state. Instead of binding input values to React state, you use a ref to access the DOM element directly when needed. This is similar to traditional HTML form behavior and may be used for simple or third-party form handling.

React Router is a standard library for routing in React applications. It allows navigation between different views or pages without reloading the browser, maintaining the single-page application (SPA) experience. Components like <BrowserRouter>, <Route>, and <Link> define navigation paths, route components, and enable smooth transitions between screens.

The <Link> component from React Router performs client-side routing, enabling smooth transitions without full-page reloads. In contrast, the <a> tag triggers a full-page reload, which breaks the SPA flow. Therefore, <Link> is preferred in React applications to maintain seamless and performant navigation.

Lifecycle methods are special functions in class components that allow developers to hook into different stages of a component’s existence—mounting, updating, and unmounting. For example:

• componentDidMount() – runs after the component is rendered.
• shouldComponentUpdate() – controls re-rendering.
• componentWillUnmount() – runs before the component is destroyed.

 These methods help in tasks like data fetching, setting timers, or cleaning up resources.

Forms are handled by controlling the input fields using state variables. Each input field is tied to a useState() variable, and its value is updated via onChange handlers. On form submission, an onSubmit handler processes or validates the data, ensuring a controlled and reliable user input flow.

Lifting state up means moving the shared state to the closest common ancestor of two or more components. This allows sibling components to access and modify the shared data through props. It promotes better data consistency and reduces duplication across components.

Conditional rendering allows components to display different elements or components based on certain conditions. It uses JavaScript logic (like if, ternary, or &&) inside JSX to render content dynamically. This helps in creating interactive and context-aware user interfaces.