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20 Important JavaScript Concepts for Your Next Interview 🚀

Jagroop Singh on November 04, 2024

When it comes to JavaScript interviews, employers are looking for practical knowledge as much as theoretical. So, here’s a list of 20 core JavaScri...

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john • Nov 4

I found Debouncing & Throttling a bit complicated for me. Is it even used in real world application or not ?
Also, I found closures interesting concept.

Jagroop Singh • Nov 4

@john12 ,
Yes, debouncing and throttling are widely used in real-world applications, especially in front-end development where performance optimization is key.

1. Debouncing

What it does: Debouncing delays the execution of a function until a certain period of inactivity has passed.
Real-world example: E-commerce sites often use debounced input on search fields to avoid overwhelming the server with queries and provide a smoother experience.

2. Throttling

What it does: Throttling, on the other hand, limits the number of times a function is executed over a set period, regardless of how often the event occurs.
Real-world example: Social media feeds or infinite scroll features often use throttling to ensure that loading more content or tracking scroll position doesn’t slow down the page.

Together, these techniques prevent “overcalling” functions, which can lead to performance issues, especially on mobile devices or slower networks.

Also,
Closures are indeed fascinating! They allow functions to retain access to their original scope, even after that scope has finished executing.

Let me know if you’d like more examples or a breakdown of any particular concept in order to unserstand it better!

sewiko • Nov 4

Wow nice and detailed explanation

Jagroop Singh • Nov 4

Thanks @hraifi

john • Nov 4

wow, you have just published another blog in the comments. Is it for real or it's GPT generated.
Well it's well explained , now I understand the whole concept of Debouncing and Throttling

Jagroop Singh • Nov 4

Thank you! Also, this response isn't generated by GPT. I personally invested time in crafting it to ensure that users can gain a better understanding of the concept.

john • Nov 4

Thank you for the efforts !!

msegmx • Nov 6

AI much? 🙄

Jagroop Singh • Nov 4

Thanks @john12

Freya • Nov 6 • Edited

That's a perfect analogy for explaining JavaScript Promises!

Here's how it breaks down:

Pending: Just like waiting for your pizza, a Promise starts in a pending state. You don’t have the result yet; it’s just a promise that something will happen, similar to how platforms like Mobcup queue content for processing.

Fulfilled: If everything goes smoothly — the pizza arrives on time — you receive what you ordered, and the Promise is fulfilled. In JavaScript, this means the Promise returns the expected result.

Rejected: Sometimes things go wrong, like a broken oven at the pizza shop. If the promise can’t be kept, it moves to a rejected state, returning an error.

Using this story, with Mobcup as a reference, makes it easy to remember: a Promise is just JavaScript’s way of saying, "I'll try to get this to you, but I’ll let you know if there’s an issue along the way."

Jagroop Singh • Nov 6

Thanks for sharing detailed explanation.

Jon Randy 🎖️ • Nov 5

A closure is a function that remembers its outer variables even after the outer function has finished executing.

Unfortunately, this is not correct.

Misconceptions About Closures

Jon Randy 🎖️ ・ Sep 27 '23

#webdev #beginners #javascript #programming

Jagroop Singh • Nov 5

Thanks for sharing and clearing misconception @jonrandy

sewiko • Nov 4

I didn't understand the concept of Promises ??

Jagroop Singh • Nov 4

okay let me explain this with a short story,
Imagine you order a pizza. The pizza shop promises it’ll arrive soon. Right now, your order is pending. After some time, either:

The pizza arrives on time, making you happy — this is the fulfilled state, and you enjoy your pizza.
Something goes wrong (like the oven breaks), so they cancel the order — this is the rejected state, leaving you without pizza.

In JavaScript, a Promise works the same way! It’s like saying, “I promise to do something later,” and based on what happens, you either get a result (fulfilled) or an error (rejected).

Jagroop Singh • Nov 4

Thanks for this nice explanation with story.

Jagroop Singh • Nov 4

Wow !!
That look's promising !!

Philip • Nov 5

Thanks for the effort! I’d like to share that EchoAPI is perfect for testing JavaScript APIs, making it easy to manage requests and responses seamlessly.

Jagroop Singh • Nov 6

Thanks for suggestion @philip_zhang_854092d88473

Tomas Stveracek • Nov 5

Great overview of key JavaScript concepts! 🚀 The examples make things easy to understand, especially closures and hoisting. Thanks for sharing this! 🙌