JavaScript

Roadmap:

Basics

  • What is JavaScript?
  • Why is JavaScript called single-threaded? (One statement at a time)
  • Hoisting?
  • let vs var vs const
    • Ref
    • SuGHaR: Scope, Global Property, Hoisting, Redeclaration
  • Functions vs Arrow Functions?
  • Explain this keyword.
  • Higher Order Function (or) Currying?
  • What is a pure function?
  • Where does the this reference point when a function (or arrow function) is written in global scope?

Async & Event Handling

  • What are callbacks?
  • What are event listeners?
  • Promise vs Async–Await?
  • Callback Hell?
  • How to convert callback to promise?
  • Asynchronous and non-blocking calls? Blocking vs synchronous?
  • How to handle multiple asynchronous calls concurrently?
  • Assert in Node.js?
  • What is the need for Promise/Async–Await even though we have callbacks?
  • Event loop: Event Queue

Functions & Closures

  • What are closures in JavaScript?
  • Coercion? (Type Coercion)
  • Symbols?
  • Iterators and Generators
  • Difference between iterables and enumerables?
  • IIFE (Immediately Invoked Function Expression)?
  • Function Currying
  • Closures — what & when to use?
  • Proxy objects?
  • Handling click events outside the target element?

DOM & Web APIs

  • What is DOM?
  • Web Components?
  • Event Bubbling and Capturing (Event Propagation / Delegation)?

Language Features

  • == vs ===
  • New ES6 features?
  • Cyclic Dependency Problem?
  • OOPs in JavaScript?
    • Inheritance: Classical & Prototype
    • Constructor function vs Class
  • call vs bind vs apply
  • Web Storage (LocalStorage, SessionStorage) & IndexedDB
  • Cookies?
  • Functional Programming & its Principles
  • Defer vs Async tag in HTML
  • Modeules: CommonJS vs AMD vs RequireJS

Module Bundlers

  • What are Module Bundlers? (Webpack, Rollup, Parcel, Snowpack, CommonJS)
    • Code Splitting in Webpack
    • Loaders: style-loader, html-loader
    • Plugins: BundleAnalyzerPlugin, etc.
    • Dev Server
    • Hot Module Replacement

Browser & Networking

  • Why does the browser send OPTIONS requests before POST/GET requests?
  • Why do we need package-lock.json?

Node.js

  • What is Node.js?
  • setTimeout vs setInterval
  • process.nextTick vs setImmediate vs setTimeout(0)
  • Reactor Pattern in Node.js
  • What are Streams? Types of Streams?
  • Buffers (Streams of binary data)
  • WebSockets
  • How to queue tasks?
    • Libraries: Bull / BullMQ

Processes & Threads

  • What is an Event in Node.js?
  • How does EventEmitter work, when should it be used?
  • How to access command line args in Node.js?
  • Parallel Processing
    • Ref
    • Child Process vs Clusters vs Worker Threads
    • Fork vs Spawn vs Exec
    • Cluster module in Node.js
  • Optimizations & scaling: Caching, Scaling, Clusters
  • What are child threads in Node.js?

Security & Best Practices

  • How to ensure npm dependencies are safe?
  • How to restrict cross-site access to cookies?
  • Side Effects: Ref

Express.js

  • What is Express?
  • What are middlewares?
  • What is next()?
  • How to pass data between middlewares?
  • Authentication & Authorization (JWT – structure & algorithm)
  • How to maintain sessions on the server side?
    • Cookies, Redis cache, express-session, others
  • Secure Cookies
  • Refresh token implementation
  • Database connections: Sequelize, Knex.js, Mongoose, Bookshelf, GooseBird
  • Loggers: Winston, Morgan
  • File Upload: Multer
  • Puppeteer: PDF generation / Headless Chrome
  • Sequelize: relationships, model hooks
  • Knex.js migrations (up & down)
  • API & DB optimizations: Node Clusters, REST optimizations, DB transactions
  • Swagger for API documentation
  • DB transaction management (auto-commit = false, rollback)
  • How to implement custom middleware?

Browser Internals

Performance

  • How to make websites fast?