10 JavaScript Interview Questions You HAVE TO KNOW

Can you pass this JavaScript interview? Here are 10 questions you should be able to answer!
Original Article - / 10-interview-questions...
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[@Diego_Cabrera]

Literally perfect timing man. I’m waiting to hear back if from my first interview and I’ll be assigned to pair program with a dev at the company. I’m quite knowledgeable but there are areas where I could brush up on. Thanks so much!

[@JamesQQuick]

Yeahhh! So glad to hear that!

[@economicist2011]

Wow, I guess I know a lot more about JS than I thought. I still have a ways to go but this is pretty encouraging.

[@slacle]

Hey James, where can I follow along for updates?

[@billyfigueroa1617]

James is an AI machine 😂 dude hit a infinite loop glitch the last 10 seconds 😂😂😂

[@ruxinqu871]

learned a lot! thanks for the video!

[@pe2062]

This was so helpful! More please!

[@simonswiss]

Thanks for making that video! I always assumed I would BOMB tech interviews and thought I'd struggle through this video. But I watched all of it, paused right after seeing the question and did my explanation. I think I nailed 9 out of 10 questions - the first one (closures) being the one I am not capable of explaining fluently. I know what closures are, but have a hard time explaining why they're important and useful. Everything else I feel like I could talk confidently about, and wouldn't be worried about digging a bit deeper if necessary. Closure, I felt like I was bullsh#tting my way through the explanation lol

[@JamesQQuick]

Love this! It's interesting how we can understand how things work but struggle to explain them sometimes. Thanks for watching and sharing your thoughts!

[@khaledsanny4817]

That rap sequence at the end 😂🔥🔥

[@JamesQQuick]

I don't know what the heck happened there lol

[@bilbobaggins3567]

Confirmed he's a cyborg.

[@pavfrang]

Thanks for the review! A pure function should not write to a file, because the file could indirectly affect state and therefore affect the result.

[@JamesQQuick]

Yeah if it's being read by another. True. Good point.

[@alanthomasgramont]

The issue I see most with people understanding promises is what actually happens during the “async” part. Most inexperienced developers don’t understand the event loop, which causes problems especially in unit testing and mocking.

[@nathangwyn6098]

I knew them all!! I'm 3.4yrs into teaching myself. I'm currently hoping between JS, TS, GO & Rust... mainly JS/Rust atm.

[@JamesQQuick]

Yeahhh! Love to hear it!

[@chandrashekar-us6ef]

What is the output of a URL on a browser for SPA vs MPA

[@ManfredSpecht]

Thanx for the cool video. I was maybe missing the new features we got in the modern ECMA-Script world, object oriented programming in JavaScript, classes vs. prototypes, maybe deeper functional things like currying and stuff. I personally do not like those kind of questions. I like a more pragmatic approach.

[@Gamewithstyle]

So nearly 50% of these are for if you’re interviewing for a react job. It’s likely you are, but it’s so important that you understand larger JavaScript concepts. There is one question about scope in this list, and it’s something juniors trip up on constantly. If you can tell me what a react hook is, but you don’t know what hoisting means, or the difference between const and let, then something went sideways at some point.

[@AlexandreMoreauLemay]

Console logging can be considered a side effect in specific situations; one of which is if you use stdin/stdout to pass values into buffers of different subprocesses. An unexpected console log can mess this up

[@Pete133]

Also if you use next.js server components then using a console log can cause the side effect of slowing your whole site down 😅

[@JamesQQuick]

bahaha this is great!!

[@incarnateTheGreat]

I never liked the Closures or Function Composition questions. Everything else for the most part seem more relevant to modern development. I suppose the first questions are more for core/library development.

[@2010giant]

I do small projects never feel like need to use Typescript...

[@1Thir13teen3]

Lol, there's a mess-up with the audio at the end

[@simonswiss]

It's the brainwashing technique to give you no choice but "check that out on James Q Quick updates" 😅

[@Pete133]

Trippin me out maaaaan 😆

[@JamesQQuick]

Yooo I have no idea what happened there lol

[@dev-akeel]

3:54 that was first thing what triggered in my mind after hearing the word "side effect".

[@deatho0ne587]

React should not even be on a top 10 of JS, due to it's very nature kind of does most of the heavy lifting for Devs. If you know the company uses a framework/library like React then learn it and it should have it's own top 10. Things that are more important and have seen newer Devs to JS in general fail on. - Primitives, Objects and Arrays - you will get some of this I think from number 4 (do not remember which number) - Testing as a whole - meaning explain the type of testing you like and if the company does something else you could pick it up - Big O(n) and why you might use for, forEach, map, set, etc... Minor most of the time (in actual coding) but when it matters it matters. Loved for interview questions though

[@wchorski]

the most important thing is to make sure you have fun

[@MichaelMooregrownman]

Wow James what are the odds with me having a 2 hour coding challenge coming up and you make this video. Thanks

[@nickwoodward819]

Pretty high that someone would :)

[@SXsoft99]

me writing tests after i've made the implementation with different test values :))

[@danielcrompton7818]

Been looking for a video like this for a while!! And the answer is I would not

[@JamesQQuick]

What do you think about these questions? Good fit?

[@danielcrompton7818]

Yeah they do!! I was interested in how to call functions without brackets!! And another thing I learned is they don’t ask very _real_ questions that would apply to real life!!

[@shinoobie1549]

Typescript is a linter for Javascript

[@JS-zm5se]

Great

[@ajiteshmishra0005]

for(var i = 1; i { console.log(i); }, 1200); } Output is 4 4 4 & for(let i = 1; i { console.log(i); }, 1200); } Output is 1 2 3 Why??

[@SeRoShadow]

My answers for the JS Interview: 1. What is a closure ? Unsafe and Unreliable scope 3. Composition, isnt that just nesting ? 5. Whats a promise ? Its own thread. 6. What is typescript ? a LSP linter and transpiler. 8,9 What is a React ? Its a JS library. 10. TDD ? Wasted effort not getting things done. Testing Prod ready code is diffrent story. Please let me know if those answers feel right.

[@UliTroyo]

3. No, it means returning functions from other functions, using closures to change the resulting function. Think of it like the opposite of inheritance: instead of “bird” inheriting from “flying animal”, you would pass the “bird” function to the “makeFlyingAnimal” function that would return a flying bird. This way, it’s easier to create for example a phoenix, because you could just pass your bird to a “resistFire” and a “reviveForever” function.

[@SeRoShadow]

@@UliTroyoI apreciate your help but ... after a little research my statement holds truth. It is function nesting, nothing more. And I consider it bad practice since you have to rewrite the code, in order, every time one step goes wrong. Not for me. Id rather do each function in its own line.

[@cotyhamilton]

That’s not what a promise is, async doesn’t mean multi-threaded

[@SeRoShadow]

​@@cotyhamiltontrue, but what would be the diffrence then ?

[@tcritt]

JS is single threaded.

[@gosnooky]

I've never, and will never consider JS to be a functional language. If you want functional, go with Haskell, Erlang, or Elixir. It has functional components to it as mentioned, but using JS in a pure functional way is restricting yourself from leveraging the full power of the language.

[@demian.succs0]

lmao

[@danielcrompton7818]

You can make functions in Javascript…?!

[@kiranpillai876]

What would consider JS then? A hybrid?

[@wisdomelue]

@@kiranpillai876yes it’s multiparadigm

[@lavalink]

Calling JS a functional language is a bit like calling myself a vegetarian just because I’m capable of eating a salad every now and then.

[@Mariojsnunes]

That's 7 JS questions

[@bloodylupin]

I just rejected a project because they don't use Typescript. I can't understand why the hell you would use JS in production in 2024, especially working in team. It's just a lot of pain.

[@Misteribel]

The questions related to functional programming concepts need a deep dive slash correction. I'm gonna assume that you know the principal ideas, but you seem a little lost in the vid. Calling JS a functional language, confusing deterministic and pure, calling logging *not* a side effect and a closure a nested function would have you lose the interview big time with serious corporations. And you really have to know your TDD, or you ain't get hired (even if companies don't use it to the letter). These questions are meant for you to fall in the trap of subtleties between the functional world and the imperative world, and you fell for the trap with eyes wide open. If you want, you can contact me, and I'll help you get the facts straight in a follow-up video.

[@AngelEduardoLopezZambrano]

Funny how you said that you don't do function composition or use it often when that's literally all you do with react. Interesting that people don't even know that.

[@UliTroyo]

Yeah, it’s unintuitive for people, but everyone who uses anything in the JS ecosystem uses it all the time. I think it’s fine; knowing the details helps, but people get adequate intuition just from using things. Kind of like music theory.

[@yega3k]

This is the problem with a language that relies too much on 3rd party libraries + frameworks to do things that should probably be built into the language. JS isn't even a real OOP language. Maybe it is nowadays, I'm not sure but when I started learning years ago, it was called "Object Based" rather than "Object Oriented". I guess TS makes it feel like OOP though. My point is that it is difficult for most devs to get below the surface of the layers and layers of libraries and frameworks so I think it is understandable if they don't know they are using something like "composition" in some project already.

[@JamesQQuick]

Yeah my point is it's not something I think about. React gives a structure for doing that. It's not a decision I make or think about.

[@scott_itall8638]

Nope, but I got the job anyway 😉

[@JamesQQuick]

lmaooo love that!

[@jkovert]

13:32 So what are you trying to say?

[@jamesgoatcher]

Damn, was hoping to see some fun nuances and idiosyncrasies of vanilla Javascript but was returned Typescript/React crap. Catfished.

[@TokyoXtreme]

I guess businesses and hiring managers aren't interested in esoteric JavaScript nuances, rather they want developers who can build projects as a team.

[@jamesgoatcher]

@@TokyoXtreme More like the illusion that they're hiring those that can. 10 years in the industry and every dev that's made an impression on me did so based on foundational knowledge. But I guess that article was probably directed towards juniors that are just task rabbits.

[@stuff3219]

What a shitty list. All of the "functional" stuff has nothing to do with javascript, and makes numeruous unfounded assertions about the superiority of functional programming. (This is a fad by the way, later we'll here about how obect oriented is actually better).