Interview Questions and Answers: SQL, Java, Python, React

Pick a technology

HTML interview questions - Structure of every web page (74 questions)
CSS interview questions - Layout, styling and responsive design (66 questions)
JavaScript interview questions - The language every frontend round is built on (83 questions)
TypeScript interview questions - JavaScript with types - required for Angular and most React jobs (38 questions)
React interview questions - Components, hooks, state and rendering (52 questions)
Angular interview questions - Components, DI, change detection, forms and signals (54 questions)
RxJS interview questions - Observables, operators and reactive streams (38 questions)
NgRx interview questions - Redux-style state management for Angular (35 questions)
SQL interview questions - Joins, grouping, window functions and indexes (52 questions)
Java interview questions - Core Java, OOP, collections, streams and threads (54 questions)
Python interview questions - Data types, functions, OOP, generators and coding problems (50 questions)

Study path by role

Fresher or junior web developer

Campus and junior rounds mostly test the basics: semantic tags and forms, the box model and Flexbox, then scope, closures and the event loop in JavaScript.

1. HTML - 2. CSS - 3. JavaScript

React developer

React questions build on JavaScript, so read closures, this and the event loop first. Then TypeScript, then React hooks, rendering and state.

1. JavaScript - 2. TypeScript - 3. React - 4. CSS

Angular developer

Angular rounds lean on TypeScript and RxJS as much as on Angular itself. Read change detection and dependency injection, then the RxJS operators, then NgRx if the job lists it.

1. TypeScript - 2. Angular - 3. RxJS - 4. NgRx

Java backend developer

Service and product companies ask core Java, OOP and collections first (HashMap internals almost always), then Java 8 streams and threads, then SQL joins and indexes. Experienced rounds add Spring Boot.

1. Java - 2. SQL

Python, data or analyst role

Expect Python data types, mutability and a short coding problem, then SQL: joins, GROUP BY with HAVING, and a window-function question such as top N per group or a running total.

1. Python - 2. SQL

Experienced frontend engineer

Senior rounds go deeper into performance and design choices: rendering and performance in React, change detection in Angular, the event loop, and CSS architecture.

1. JavaScript - 2. React - 3. Angular - 4. CSS

What each topic covers

HTML interview questions

CSS interview questions

CSS fundamentals (12)
Box model and sizing (12)
Positioning and stacking (7)
Flexbox (8)
CSS Grid (7)
Responsive design (6)
Transitions, animation and performance (6)
Architecture and modern CSS (8)

JavaScript interview questions

Types and values (13)
Scope, hoisting and closures (9)
this, functions and objects (15)
Arrays and objects in practice (10)
Event loop and asynchronous JavaScript (14)
DOM and browser (12)
Tricky and output-based questions (10)

TypeScript interview questions

React interview questions

Angular interview questions

RxJS interview questions

NgRx interview questions

Core ideas (7)
Actions and reducers (7)
Selectors (5)
Effects (7)
Entity, feature APIs and alternatives (9)

SQL interview questions

SQL basics (8)
Filtering and querying (9)
Joins (7)
Grouping, subqueries and common query problems (8)
Window functions (6)
Indexes, transactions and design (14)

Java interview questions

Python interview questions

How to use this hub

Read the section, not the whole page

Each topic is split into sections. Before an interview, read the two or three sections the role actually needs - change detection for Angular, hooks for React, the event loop for JavaScript.

Say the answer out loud

These answers are written the length a spoken answer should be: two or three sentences, then an example. Practise saying them, not reading them.

Follow the example

Where a question has code, type it into a sandbox and break it on purpose. You remember what you debug far longer than what you read.