Interview Questions

More code, larger bundle (also after minification), this context, logic split across multiple methods (componentDidMount/Update/WillUnmount versus useEffect)

Portals let your components render some of their children into a different place in the DOM.

requires interpreter?? dynamic, high-level, multi-paradigm, prototype based, single-threaded

enum vs custom enum typeof/ keyof const

util types

"as" keyword

any, unknown, never

Difference between interface and type. Interface can be applied for any object (fn, class, object), can be extended, interfaces with the same name will be merged. Type can be used union/ intersection

to check fn

What is virtualization?

this

Pure function - ideal function which determined (for the same input - same output as in math) and without side effects (Interaction with outer environment, increment/ decrement, read/write operations, var/const changes). DOM manipulations, API calls, Timers, external state changes

Core Web Vitals are metrics that measure user experience: LCP (Largest Contentful Paint), FID (First Input Delay), and CLS (Cumulative Layout Shift). They impact SEO and user satisfaction.

Context provides a way to pass data through the component tree without having to pass props down manually at every level. It''s useful for global data like themes, user info, or language preferences.

Flexbox is for one-dimensional layouts (row or column). Grid is for two-dimensional layouts (rows and columns). Use Flexbox for navigation bars, Grid for page layouts.

Local state (useState), Context API (light global state), Redux (predictable state container), Zustand (simple stores), Recoil (atomic state), React Query (server state). Choose based on complexity.

SSR generates HTML on the server for each request, improving SEO and initial load. Next.js supports SSR with getServerSideProps. Contrast with Static Site Generation (SSG) which builds at build time.

The Virtual DOM is a lightweight copy of the actual DOM. React uses it to optimize updates by comparing the virtual DOM with the real DOM and only updating what changed (reconciliation).

Generics allow you to write reusable code that works with multiple types while maintaining type safety. They''re denoted with angle brackets like `<T>` and act as type variables. Parametrized polymorphism

Interfaces can be extended and merged, making them better for object shapes and classes. Types are more flexible and can represent unions, intersections, and primitives. Prefer interfaces for object shapes.

TypeScript provides built-in utility types like Partial<T>, Required<T>, Pick<T, K>, Omit<T, K>, Record<K, T>, etc. They help transform types without rewriting them.

Lazy loading defers loading of non-critical resources until needed. Code splitting breaks your bundle into smaller chunks loaded on demand, improving initial load time. Use React.lazy() and dynamic imports.

"==" - converts types before comparing values (5 == "5" → true), "===" - compares both value AND type without conversion