10 Types of API Testing

Big Data Pipelines on the Cloud

Session, JWT, SSO, and OAuth 2.0 in One Diagram

Key Database Sharding Concepts

API Security 101

Because you asked for it: Deep Learning Notes

✅ Top 50 JavaScript Interview Questions 💻✨

1. What are the key features of JavaScript? 
2. Difference between var, let, and const 
3. What is hoisting? 
4. Explain closures with an example 
5. What is the difference between == and ===? 
6. What is event bubbling and capturing? 
7. What is the DOM? 
8. Difference between null and undefined 
9. What are arrow functions? 
10. Explain callback functions 
11. What is a promise in JS? 
12. Explain async/await 
13. What is the difference between call, apply, and bind? 
14. What is a prototype? 
15. What is prototypal inheritance? 
16. What is the use of ‘this’ keyword in JS? 
17. Explain the concept of scope in JS 
18. What is lexical scope? 
19. What are higher-order functions? 
20. What is a pure function? 
21. What is the event loop in JS? 
22. Explain microtask vs. macrotask queue 
23. What is JSON and how is it used? 
24. What are IIFEs (Immediately Invoked Function Expressions)? 
25. What is the difference between synchronous and asynchronous code? 
26. How does JavaScript handle memory management? 
27. What is a JavaScript engine? 
28. Difference between deep copy and shallow copy in JS 
29. What is destructuring in ES6? 
30. What is a spread operator? 
31. What is a rest parameter?
32. What are template literals? 
33. What is a module in JS? 
34. Difference between default export and named export 
35. How do you handle errors in JavaScript? 
36. What is the use of try...catch? 
37. What is a service worker? 
38. What is localStorage vs. sessionStorage? 
39. What is debounce and throttle? 
40. Explain the fetch API 
41. What are async generators? 
42. How to create and dispatch custom events? 
43. What is CORS in JS? 
44. What is memory leak and how to prevent it in JS? 
45. How do arrow functions differ from regular functions? 
46. What are Map and Set in JavaScript? 
47. Explain WeakMap and WeakSet 
48. What are symbols in JS? 
49. What is functional programming in JS? 
50. How do you debug JavaScript code?

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Because you asked for it: Deep Learning Interview Questions

#Paper
What Every Programmer Should Know About Memory
You must read this paper.

Git Basics

SOAP vs REST vs GraphQL vs RPC

Visualizing SQL Queries

Note: The actual execution sequence may differ from this mental model due to optimization strategies employed by the query optimizer.

SQL Question:

What does this query return for a NULL score?

What is API Gateway?

✅ 50 Must-Know Web Development Concepts for Interviews 🌐💼

📍 HTML Basics 
1. What is HTML? 
2. Semantic tags (article, section, nav) 
3. Forms and input types 
4. HTML5 features 
5. SEO-friendly structure 

📍 CSS Fundamentals 
6. CSS selectors & specificity 
7. Box model 
8. Flexbox 
9. Grid layout 
10. Media queries for responsive design 

📍 JavaScript Essentials
11. let vs const vs var 
12. Data types & type coercion 
13. DOM Manipulation 
14. Event handling 
15. Arrow functions 

📍 Advanced JavaScript 
16. Closures 
17. Hoisting 
18. Callbacks vs Promises 
19. async/await 
20. ES6+ features 

📍 Frontend Frameworks
21. React: props, state, hooks 
22. Vue: directives, computed properties 
23. Angular: components, services 
24. Component lifecycle 
25. Conditional rendering 

📍 Backend Basics
26. Node.js fundamentals 
27. Express.js routing 
28. Middleware functions 
29. REST API creation 
30. Error handling 

📍 Databases 
31. SQL vs NoSQL 
32. MongoDB basics 
33. CRUD operations 
34. Indexes & performance 
35. Data relationships 

📍 Authentication & Security 
36. Cookies vs LocalStorage 
37. JWT (JSON Web Token) 
38. HTTPS & SSL 
39. CORS 
40. XSS & CSRF protection 

📍 APIs & Web Services
41. REST vs GraphQL 
42. Fetch API 
43. Axios basics 
44. Status codes 
45. JSON handling 

📍 DevOps & Tools 
46. Git basics & GitHub 
47. CI/CD pipelines 
48. Docker (basics) 
49. Deployment (Netlify, Vercel, Heroku) 
50. Environment variables (.env)

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✅ HTML Basics – Interview Questions & Answers 📄

1️⃣ What is HTML?
Answer: HTML (HyperText Markup Language) is the standard language used to structure content on the web. It defines elements like headings, paragraphs, links, images, and forms using tags.

2️⃣ What are semantic tags in HTML?
Answer: Semantic tags clearly describe their meaning in the context of the page. Examples:
- <article> – for self-contained content
- <section> – for grouped content
- <nav> – for navigation links
They improve accessibility and SEO.

3️⃣ What are forms and input types in HTML?
Answer: Forms collect user input. Common input types include:
- text, email, password, checkbox, radio, submit
Example:

<form>
  <input type="email" placeholder="Enter your email" />
</form>

4️⃣ What are key features of HTML5?
Answer:
- New semantic tags (<header>, <footer>, <main>)
- Native audio/video support (<audio>, <video>)
- Local storage & session storage
- Canvas for graphics
- Geolocation API

5️⃣ How do you create an SEO-friendly HTML structure?
Answer:
- Use semantic tags
- Include proper heading hierarchy (<h1> to <h6>)
- Add alt attributes to images
- Use denoscriptive noscripts and meta tags
- Ensure fast loading and mobile responsiveness

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✅ CSS Fundamentals – Interview Questions & Answers 🎨🧠

1️⃣ What is the Box Model in CSS?
The box model describes how elements are rendered: 
Content -> Padding -> Border -> Margin
It affects spacing and layout.

2️⃣ What’s the difference between ID and Class selectors?
- #id: Unique, used once. 
- .class: Reusable across multiple elements. 
Example: 

#header { color: red; }  
.card { padding: 10px; }

3️⃣ How does CSS Specificity work? 
Specificity decides which styles are applied when multiple rules target the same element. 
Hierarchy: 
Inline > ID > Class > Element 
Example: 

<p id="one" class="two">Text</p>

#one has higher specificity than .two.

4️⃣ What is Flexbox?
A layout model for 1D alignment (row or column). 
Key properties: 
- display: flex
- justify-content, align-items,
flex-wrap

5️⃣ Difference between Flexbox and Grid?
- Flexbox: 1D layout (row/column). 
- Grid: 2D layout (rows & columns). 
Use Grid when layout needs both directions.

6️⃣ What are Media Queries? 
Used to create responsive designs based on screen size/device. 
Example: 

@media (max-width: 600px) {
  body { font-size: 14px; }
}

7️⃣ How do you center a div using Flexbox? 

.container {
  display: flex;
  justify-content: center;
  align-items: center;
}

8️⃣ What is the difference between position: relative and absolute?
- relative: positions relative to itself. 
- absolute: positions relative to the nearest positioned ancestor.

9️⃣ Explain z-index in CSS. 
Controls stacking order of elements. Higher z-index = appears on top.

🔟 How can you optimize CSS performance? 
- Minify files 
- Use shorthand properties 
- Combine selectors 
- Avoid deep nesting 
- Use external stylesheets

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✅ JavaScript Essentials – Interview Questions with Answers🧠💻 

1️⃣ Q: What is the difference between let, const, and var?
A: 
- var: Function-scoped, hoisted, can be redeclared. 
- let: Block-scoped, not hoisted like var, can't be redeclared in same scope. 
- const: Block-scoped, must be assigned at declaration, cannot be reassigned.

2️⃣ Q: What are JavaScript data types? 
A:
- Primitive types: string, number, boolean, null, undefined, symbol, bigint 
- Non-primitive: object, array, function 
Type coercion: JS automatically converts between types in operations ('5' + 2 → '52')

3️⃣ Q: How does DOM Manipulation work in JS?
A:
The DOM (Document Object Model) represents the HTML structure. JS can access and change elements using: 
- document.getElementById() 
- document.querySelector() 
- element.innerText, element.innerHTML, element.style etc.

4️⃣ Q: What is event handling in JavaScript?
A: 
It allows reacting to user actions like clicks or key presses. 
Example: 

document.getElementById("btn").addEventListener("click", () => {
  alert("Button clicked!");
});

5️⃣ Q: What are arrow functions?
A:
A shorter syntax for functions introduced in ES6. 

const add = (a, b) => a + b;

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✅ Advanced JavaScript Interview Questions with Answers 💼🧠

1. What is a closure in JavaScript?
A *closure* is a function that has access to its outer function's variables, even after the outer function has returned.

function outer() {
  let count = 0;
  return function inner() {
    count++;
    console.log(count);
  }
}
const counter = outer();
counter(); // 1
counter(); // 2

2. Explain event delegation.
Event delegation is a technique where you attach a single event listener to a parent element to handle events on its child elements using event.target.

3. What is the difference between == and ===? 
- == checks for value equality (type coercion allowed). 
- === checks for both value and type (strict equality). 

'5' == 5   // true  
'5' === 5  // false

4. What is the "this" keyword?
this refers to the object that is executing the current function. In arrow functions, this is lexically bound (based on where it's defined).

5. What are Promises? 
Promises handle asynchronous operations. They have 3 states: *pending, resolved, rejected*.

const p = new Promise((resolve, reject) => {
  resolve("Success");
});
p.then(console.log);

6. Explain async/await.
Syntactic sugar over Promises for better readability in async code.

async function fetchData() {
  const res = await fetch(url);
  const data = await res.json();
}

7. What is hoisting?
Variables and function declarations are moved to the top of their scope before code execution.

console.log(a); // undefined
var a = 5;

8. What are arrow functions and how do they differ? 
Arrow functions are shorter and do not have their own this, arguments, or super.

const add = (a, b) => a + b;

9. What is the event loop?
The event loop handles asynchronous callbacks and ensures non-blocking behavior in JS by placing them in the task queue after the call stack is clear.

10. What are IIFEs (Immediately Invoked Function Expressions)?
Functions that run as soon as they are defined.

(function() {
  console.log("Runs immediately");
})();

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