Here is a great JavaScript interview question!

What the heck is a Promise doing under the hood?

In JavaScript, things usually happen one after the other. It's like a checklist each item gets done before moving to the next.

When a function returns a Promise, it's like making a promise to do something, like fetch data from the internet. But JavaScript doesn't wait around for the data to come back. Instead, it moves on to the next task.

Now, here's where things get interesting. While JavaScript is busy doing other stuff, like running more code, the Promise is off fetching data in the background.

Once the data is fetched, the Promise is fulfilled, and it has some information to share. But JavaScript needs to know when it's time to handle that information. That's where the onFulfilled part of the Promise comes in.

When the Promise is fulfilled, JavaScript takes the onFulfilled code and puts it in a special queue, ready to be run.

Now, async/await enters the scene. When we mark a function as async, we're telling JavaScript, "Hey, this function might take some time to finish, so don't wait up for it."

And when we use the await keyword inside an async function, it's like saying, "Hold on a sec, JavaScript. I need to wait for something important before moving on."

So, when JavaScript encounters an await keyword, it pauses and lets the async function do its thing. If that thing happens to be a Promise, JavaScript knows it can move on to other tasks while waiting for the Promise to resolve.

Once the Promise is resolved, JavaScript picks up where it left off and continues running the code.

Promises and async/await allow JavaScript to handle asynchronous tasks while keeping things organized and in order. Promises handle the background tasks, while async/await makes it easier to work with them in our code, ensuring everything happens in the right sequence.

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⌨️ JavaScript Array methods

𝟏. 𝐉𝐚𝐯𝐚𝐒𝐜𝐫𝐢𝐩𝐭+𝐑𝐞𝐚𝐜𝐭
Front-end web development
𝟐. 𝐉𝐚𝐯𝐚𝐒𝐜𝐫𝐢𝐩𝐭+𝐀𝐧𝐠𝐮𝐥𝐚𝐫
Front-end web development
𝟑. 𝐉𝐚𝐯𝐚𝐒𝐜𝐫𝐢𝐩𝐭+𝐕𝐮𝐞.𝐣𝐬
Front-end web development
𝟒. 𝐇𝐓𝐌𝐋+𝐂𝐒𝐒
Basic web structure and styling
𝟓. 𝐉𝐚𝐯𝐚𝐒𝐜𝐫𝐢𝐩𝐭+𝐍𝐨𝐝𝐞.𝐣𝐬:
Back-end development
𝟔. 𝐏𝐲𝐭𝐡𝐨𝐧+𝐃𝐣𝐚𝐧𝐠𝐨
Web development (back-end)
𝟕. 𝐏𝐲𝐭𝐡𝐨𝐧+𝐅𝐥𝐚𝐬𝐤
Web development (back-end)
𝟖. 𝐉𝐚𝐯𝐚+𝐒𝐩𝐫𝐢𝐧𝐠 𝐁𝐨𝐨𝐭
Enterprise-level back-end development

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In JavaScript, a Proxy is an object that allows you to intercept and redefine fundamental operations for another object. This enables custom behavior for things like property access, function calls, and more. Proxies are part of ECMAScript 6 (ES6) and provide a way to control how an object interacts with the rest of your code.

Here are the 50 JavaScript interview questions for 2024

1. What is JavaScript?
2. What are the data types in JavaScript?
3. What is the difference between null and undefined?
4. Explain the concept of hoisting in JavaScript.
5. What is a closure in JavaScript?
6. What is the difference between “==” and “===” operators in JavaScript?
7. Explain the concept of prototypal inheritance in JavaScript.
8. What are the different ways to define a function in JavaScript?
9. How does event delegation work in JavaScript?
10. What is the purpose of the “this” keyword in JavaScript?
11. What are the different ways to create objects in JavaScript?
12. Explain the concept of callback functions in JavaScript.
13. What is event bubbling and event capturing in JavaScript?
14. What is the purpose of the “bind” method in JavaScript?
15. Explain the concept of AJAX in JavaScript.
16. What is the “typeof” operator used for?
17. How does JavaScript handle errors and exceptions?
18. Explain the concept of event-driven programming in JavaScript.
19. What is the purpose of the “async” and “await” keywords in JavaScript?
20. What is the difference between a deep copy and a shallow copy in JavaScript?
21. *PH4N745M*
21. How does JavaScript handle memory management?
22. Explain the concept of event loop in JavaScript.
23. What is the purpose of the “map” method in JavaScript?
24. What is a promise in JavaScript?
25. How do you handle errors in promises?
26. Explain the concept of currying in JavaScript.
27. What is the purpose of the “reduce” method in JavaScript?
28. What is the difference between “null” and “undefined” in JavaScript?
29. What are the different types of loops in JavaScript?
30. What is the difference between “let,” “const,” and “var” in JavaScript?
31. Explain the concept of event propagation in JavaScript.
32. What are the different ways to manipulate the DOM in JavaScript?
33. What is the purpose of the “localStorage” and “sessionStorage” objects?
34. How do you handle asynchronous operations in JavaScript?
35. What is the purpose of the “forEach” method in JavaScript?
36. What are the differences between “let” and “var” in JavaScript?
37. Explain the concept of memoization in JavaScript.
38. What is the purpose of the “splice” method in JavaScript arrays?
39. What is a generator function in JavaScript?
40. How does JavaScript handle variable scoping?
41. What is the purpose of the “split” method in JavaScript?
42. What is the difference between a deep clone and a shallow clone of an object?
43. Explain the concept of the event delegation pattern.
44. What are the differences between JavaScript’s “null” and “undefined”?
45. What is the purpose of the “arguments” object in JavaScript?
46. What are the different ways to define methods in JavaScript objects?
47. Explain the concept of memoization and its benefits.
48. What is the difference between “slice” and “splice” in JavaScript arrays?
49. What is the purpose of the “apply” and “call” methods in JavaScript?
50. Explain the concept of the event loop in JavaScript and how it handles asynchronous operations.

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Here are some common frontend interview questions along with brief answers:

1. What is the DOM (Document Object Model)?
- Answer: The DOM is a programming interface for web documents. It represents the structure of a web page and allows scripts to dynamically access and update the content, structure, and style of a webpage.

2. Explain the difference between null and undefined in JavaScript.
- Answer: null represents the intentional absence of any object value, while undefined represents a variable that has been declared but has not been assigned a value.

3. What are closures in JavaScript?
- Answer: Closures are functions that remember the scope in which they were created, even after that scope has exited. They have access to variables from their containing function's scope.

4. Describe the differences between CSS Grid and Flexbox.
- Answer: CSS Grid is a two-dimensional layout system, while Flexbox is one-dimensional. Grid is used for overall layout structure, while Flexbox is ideal for distributing space and aligning items within a container along a single axis.

5. What is responsive web design, and how do you achieve it?
- Answer: Responsive web design is an approach to design and coding that makes web pages render well on various devices and screen sizes. Achieve it through media queries, flexible grids, and fluid images.

6. Explain the "box model" in CSS.
- Answer: The box model describes how elements on a web page are rendered. It consists of content, padding, border, and margin, and these properties determine the element's total size.

7. How does the event delegation work in JavaScript?
- Answer: Event delegation is a technique where you attach a single event listener to a common ancestor of multiple elements instead of attaching listeners to each element individually. Events that bubble up from child elements can be handled by the ancestor.

8. What is the purpose of the localStorage and sessionStorage objects in JavaScript?
- Answer: Both localStorage and sessionStorage allow you to store key-value pairs in a web browser. The key difference is that data stored in localStorage persists even after the browser is closed, whereas data in sessionStorage is cleared when the session ends (e.g., when the browser is closed).

9. Explain the same-origin policy in the context of web security.
- Answer: The same-origin policy is a security measure that restricts web pages from making requests to a different domain (protocol, port, or host) than the one that served the web page. It helps prevent cross-site request forgery (CSRF) and other security vulnerabilities.

10. What are the benefits of using a CSS preprocessor like Sass or Less?
- Answer: CSS preprocessors provide benefits such as variables, nesting, functions, and mixins, which enhance code reusability, maintainability, and organization. They allow you to write cleaner and more efficient CSS.

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Sample email template to reach out to HR’s as fresher

Hi Jasneet,

I recently came across your LinkedIn post seeking a React.js developer intern, and I am writing to express my interest in the position at Airtel. As a recent graduate, I am eager to begin my career and am excited about the opportunity.

I am a quick learner and have developed a strong set of dynamic and user-friendly web applications using various technologies, including HTML, CSS, JavaScript, Bootstrap, React.js, Vue.js, PHP, and MySQL. I am also well-versed in creating reusable components, implementing responsive designs, and ensuring cross-browser compatibility.

I am confident that my eagerness to learn and strong work ethic will make me an asset to your team.

I have attached my resume for your review. Thank you for considering my application. I look forward to hearing from you soon.

Thanks!

I hope you will found this helpful 🙂

⌨️ JavaScript: Array Methods Visualized