hello.frontend
Mastery Path

150 Questions: The Pro

Deep dive into performance, architecture, and system design.

Roadmap notes

Capture module-level gaps, repeated mistakes, and what to review before continuing.

1

Module 1: Foundations

Phase 1 of your journey.

4. Improve a function

PRO
mediumcoding
Facebook

How do you check if an object has a property?

mediumcoding

5. Throttle

mediumcoding
Adobe
Airbnb
Amazon
+15

Classical vs prototypal inheritance

easycoding

13. Deep Clone

mediumcoding

AbortController — cancelling async work the right way

mediumcoding

14. Event Emitter

PRO
mediumcoding
Facebook

How do you reliably check if an object is empty?

mediumcoding

66. Promise Methods

PRO
easycoding
ClickUp
Facebook
LinkedIn

How do you check the data type of a variable?

mediumcoding

19. Memoize I

easycoding
Facebook

Anonymous functions — what they are and where they shine

mediumcoding

86. API Retry

PRO
mediumcoding
Atlassian

Why array indices make bad React keys

mediumcoding

Polyfill: call( )

PRO
mediumcoding
2

Module 2: Advanced Patterns

Phase 2 of your journey.

aria-label, aria-labelledby, and aria-live in practice

mediumcoding

mul(a)(b)(c)

easycoding

async/await — syntactic sugar over promises

hardcoding

sum(a)(b)(c).....(n)

mediumcoding

How to test asynchronous code without flaky tests

mediumcoding

Flatten Array

easycoding

What are common async data loading patterns in React?

easycoding

Polyfill: map( )

easycoding

What are React Fragments used for?

easycoding

City Fetcher API

PRO
easycoding

How does the box model work in CSS?

mediumcoding

promise.all( )

PRO
hardcoding

What is React hydration?

hardcoding

promise.allSettled( )

PRO
hardcoding

How do you iterate over object properties?

mediumcoding
3

Module 3: Mastery

Phase 3 of your journey.

promise.any( )

PRO
hardcoding

What does box-sizing: border-box mean?

mediumcoding

promise.race( )

PRO
hardcoding

What is difference between sync and async function?

mediumcoding

Reverse Words in a String

easycoding

What is the difference between React Node, React Element, and React Component?

mediumcoding

promise.reject()

easycoding

What are the benefits of using hooks in React?

easycoding

composeAsync

PRO
mediumcoding

What tools help find security vulnerabilities?

easycoding

Sequential Async

PRO
mediumcoding

What are React Portals?

mediumcoding

Debounce II

PRO
mediumcoding
Amazon
Flipkart
Google
+2

How does caching improve performance?

mediumcoding

Promise Merge

PRO
mediumcoding
Meta
4

Module 4: Mastery

Phase 4 of your journey.

How do you decide between React state, context, and external state managers?

easycoding

Chunk

PRO
easycoding

What is the difference between call( ) and bind( )?

mediumcoding

Polyfill: Array.prototype.reduce

easycoding
Amazon
Apple
ByteDance

What are callback functions?

easycoding

JSON.stringify (Basic)

mediumcoding

What is the difference between call( ) and apply( )?

mediumcoding

JSON.stringify II (Advanced)

PRO
hardcoding
Google
Snap

What is the prototype pattern?

easycoding

React Hook: useTimeout

PRO
mediumcoding

What is the difference between Client side rendering and Server side rendering?

mediumcoding

Fill

PRO
easycoding

What is the Beacon API?

mediumcoding

Data Merging (Gym Sessions)

PRO
mediumcoding
Stripe

Using closures for private variables

easycoding
5

Module 5: Mastery

Phase 5 of your journey.

React Tic-Tac-Toe Engine

mediummachine
Google
Microsoft
Uber

What are common data fetching pitfalls in React?

hardcoding

Performant Image Slider

mediummachine
Amazon
Google
Meta

What AJAX actually means today

mediumcoding

API Search and Render Image

PRO
mediummachine
Google
Meta

What is code coverage?

hardcoding

Accessible React Tabs

easymachine
Airbnb
Meta

querySelector vs getElementById

hardcoding

Recursive File Explorer

mediummachine
Google
Meta

CommonJS vs ES Modules

mediumcoding

Build a Resilient Test Runner

hardcoding

Common 'this' pitfalls

mediumcoding

Traffic Light

Mediummachine
Google
Meta

Explain the composition pattern in React

easycoding

Star Rating

PRO
Easymachine
Google
Meta
6

Module 6: Mastery

Phase 6 of your journey.

What is Cross-Site Scripting (XSS)?

mediumcoding

Accordion

Easymachine
Google
Meta

How do you organize code in a JavaScript project?

easycoding

Auto-complete

PRO
Hardmachine
Amazon
Google

What is clickjacking and how do you prevent it?

mediumcoding

Modal System

Mediummachine
Google
Meta

Critical Rendering Path

mediumcoding
Google
Meta
Netflix

Pagination

PRO
Mediummachine
Google
Uber

What is CSRF?

easycoding

Multi-step Form

Mediummachine
Amazon
Meta

What is the CSS display property and what are examples of its use?

mediumcoding

Toast Notification

PRO
Hardmachine
Google
Meta

What is callback hell?

hardcoding

Virtual List (Windowing)

PRO
Hardmachine
Google
Netflix

What is CSS selector specificity and how does it work?

hardcoding
7

Module 7: Mastery

Phase 7 of your journey.

Custom Query Hook

PRO
Hardmachine
Google
Uber

What are the pros and cons of compiling to JavaScript?

hardcoding

Kanban Board (DnD)

Hardmachine
Meta
Uber

What are the pros and cons of CSS preprocessors?

hardcoding

Nested Checkboxes (Tri-state)

PRO
Hardmachine
Amazon
Meta

What do you like and dislike about CSS preprocessors?

hardcoding

Product Dashboard

PRO
Hardmachine
Amazon

How does positioning work in CSS?

mediumcoding

Form Builder (JSON Schema)

PRO
Hardmachine
Google
Meta

What is the command pattern?

easycoding

Infinite Scroll

PRO
Hardmachine
Google
Meta

How do you handle browser-specific styling issues?

mediumcoding

Analog Clock

PRO
Mediummachine
Meta

What is the difference between controlled and uncontrolled components in React?

easycoding

Memory Game

PRO
Hardmachine
Google
8

Module 8: Mastery

Phase 8 of your journey.

default vs named export

mediumcoding

Poll Widget

PRO
Mediummachine
Meta

What is a static method in a class?

easycoding

Transfer List

PRO
Hardmachine
Meta

How do you debug React applications?

mediumcoding

Progress Bar

PRO
Easymachine
Google

What is the difference between debouncing and throttling?

easycoding

Global Scope, Function Scope, and Block Scope

hardcoding

What is dangerouslySetInnerHTML and why is it dangerous?

mediumcoding

How do you optimize DOM manipulation?

mediumcoding

What is doctype in HTML in start of HTML file?

mediumcoding

Why is document.write() considered bad practice?

hardcoding

Attribute vs property in the DOM

mediumcoding

What is currying in JavaScript?

easycoding

What is the Constraint Validation API?

mediumcoding
9

Module 9: Mastery

Phase 9 of your journey.

What is the event loop in JavaScript?

mediumcoding

What are common CSS efficiency gotchas?

easycoding

How do you handle errors in asynchronous operations?

mediumcoding

What are ES2015 classes and how do they differ from ES5 function constructors?

hardcoding

What is event delegation in JavaScript?

mediumcoding

What are error boundaries in React?

easycoding

Error handling with try...catch

hardcoding

How does error propagation work in JavaScript?

mediumcoding

Describe event capturing in JavaScript

mediumcoding

What is forwardRef() in React?

hardcoding

What are default parameters?

mediumcoding

What CSS frameworks have you used?

hardcoding

What is difference between a map object and a plain object in JavaScript?

mediumcoding

Why are functions first-class objects?

mediumcoding

What data structure is used to represent the DOM?

easycoding
10

Module 10: Mastery

Phase 10 of your journey.

What is the decorator pattern?

easycoding

What is destructuring assignment?

mediumcoding

What is the purpose of break and continue?

easycoding

Hoisting pitfalls and how to avoid them

mediumcoding

How do you create a constructor function?

easycoding

How to prevent the UI from blocking during a long running task?

mediumcoding

How would you style an SVG?

easycoding

What is Cross-Origin Resource Sharing (CORS)?

easycoding

Where should CSS links and JS scripts be placed in HTML?

mediumcoding

How do iframes communicate with the parent page?

mediumcoding

Why is input validation important?

mediumcoding

What are the HTTP methods?

mediumcoding

How would you implement dark mode and light mode?

easycoding

Why does React recommend against mutating state?

hardcoding

What are iterators and generators in JavaScript?

easycoding