Most interviews in India start with fundamentals: var/let/const, hoisting, closures, the event loop, == vs ===, callbacks vs promises vs async/await, array methods like map/filter/reduce, and debouncing. Instead of memorising answers, prepare a small code snippet for each concept so you can demonstrate it. Interviewers almost always follow up with "why", so depth on a few core topics beats shallow coverage of many.

For freshers, expect basics: difference between let, const and var, arrow functions vs normal functions, array and string methods, simple output-prediction questions, and DOM manipulation. You will usually get one or two live coding tasks, like reversing a string or flattening an array. Recruiters for entry-level roles focus on fundamentals plus one framework, usually React, so a couple of solid projects matter more than a long list of answers.

A Promise is an object representing the eventual completion or failure of an asynchronous operation. It has three states — pending, fulfilled and rejected — and results are handled with .then/.catch or async/await. Interviewers commonly ask you to chain promises, explain the difference between Promise.all, Promise.allSettled and Promise.race, and convert callback-based code into promise-based code.

A closure is a function that remembers the variables from the scope where it was created, even after that outer function has finished executing. Closures power data privacy, function factories and module patterns in plain JavaScript. In React, they explain how event handlers and hooks capture values between renders — and why you sometimes see "stale" values inside a callback, which is a favourite interview follow-up.

These questions appear constantly in frontend interviews, and the reliable way to prepare is deliberate practice: take small snippets on hoisting, closures, this binding, type coercion and the event loop, predict the output on paper, then run the code to verify. Maintain a notebook of every question you get wrong and revisit it weekly. Focus especially on setTimeout inside loops, implicit coercion with ==, and the execution order of synchronous code, microtasks and macrotasks.

useState is the hook that adds local state to a function component. Calling it returns two things: the current state value and a setter function, and updating state through the setter schedules a re-render. Common beginner mistakes are mutating state directly instead of replacing it, and assuming the state variable updates immediately on the next line — it only changes on the next render.

useEffect is meant for synchronising a component with systems outside React — data fetching, subscriptions, timers, or direct DOM access. Problems start when it is used to derive state that could simply be computed during render, or to respond to one state change by setting another, which creates extra render cycles and possible race conditions. Before adding an effect, ask whether the value can be calculated from existing props and state — very often it can.

A good beginner tutorial should go beyond a counter example and cover useState, useEffect with dependency arrays, conditional rendering, forms with controlled inputs, and at least one custom hook built from scratch. It should also explain the rules of hooks — call them only at the top level of a component — and show real UIs like a search filter or a todo list. After following along, rebuild the same examples without looking, because that is where the actual learning happens.

You can start React once you are comfortable with functions, arrays and objects, ES6 features like destructuring, spread and template literals, array methods, and the basics of asynchronous JavaScript with promises. Concepts like closures and the this keyword matter too, because React leans on them heavily. You do not need to master advanced JavaScript first — many people learn the two in parallel — but weak fundamentals are the most common reason React feels confusing.

Start once your JavaScript fundamentals are comfortable, because TypeScript builds directly on them. Learn in this order: basic types, interfaces and type aliases, unions and generics, then narrowing and utility types, keeping the compiler's strict mode on from day one. The fastest way to make it stick is to convert small JavaScript projects — a to-do app or a small API module — into TypeScript and fix every error the compiler points out.

For most frontend roles, yes — arrays, strings, objects, linked lists, trees and basic recursion cover the majority of frontend interview rounds, and JavaScript is accepted on all major coding practice platforms. For product-based companies, add dynamic programming and graph basics. The bigger differentiator for frontend candidates is usually strong JavaScript fundamentals and framework depth, so balance DSA practice with React and browser concepts rather than grinding DSA alone.

A JSON Web Token is a signed token that carries claims like the user's ID and expiry, so the server can verify who you are without storing session state. After login, the frontend stores the token and sends it in the Authorization header with each API request. Be ready to discuss where to store it — localStorage is convenient but vulnerable to XSS, while httpOnly cookies are safer — and how short-lived access tokens pair with refresh tokens.

Web Vitals are a set of metrics that measure real user experience: Largest Contentful Paint for loading speed, Interaction to Next Paint for responsiveness, and Cumulative Layout Shift for visual stability. They affect both user experience and search rankings, which is why they now show up in frontend interviews. Practically, improve them by compressing and lazy-loading images, reducing and code-splitting JavaScript bundles, and reserving space for dynamic content to prevent layout shifts.

Frontend hiring is one of the most skills-driven areas of tech, so a degree is rarely the deciding factor. What moves the needle is a portfolio of deployed projects on GitHub, a solid grasp of JavaScript and at least one framework, and the ability to explain your code clearly in interviews. Many companies shortlist candidates through coding rounds and practical tasks rather than filtering by degree alone.