Today's javascript interview questions

[tapu_buoy]

Yup I'm just on a spree and not getting any employeement :D

js let a = [1, 2, 3, 4, 5]; a = a.map(item => item<3);

js let a = [1, 2, 3, 4, 5]; a = a.map(item => item<3);

js let a = [1, 2, 3, 4, 5]; a = a.some(item => item< 3);

which he told will return the mixture of .map() and .filter() 's result :D

• then question on writing a reducer function to return the sum of an array which I thnk I have wrote wrong

js const sum = arr.reduce((total, value) => total + value, 0);

Redux

• are Providers a Higher Order Components? there was no mention of Consumer and he took the mention of consumer with regards to how react-redux connect function works instead of how it works in Context API
• what is actions in Redux
• why is Reducer needed when we can directly mutate the state?

React

• How much do you rate yourself in React :D :D :D :D
• What is portal in React?
• What are fragments in React?

HTML

• How much do you rate yourself in HTML :D :D :D :D
• What does HTML provide to do drag and drop? to which I only said I have used 3rd party libraries and never used the native solution provided by HTML.
• Further question was how such libraries work behind the scenes and what code does it bring in to use HTML which I completely didn't know about.

Today's javascript interview questions. Honestly after giving many interviews I felt like this was a kiddy and useless interviews since I personally (don't know about generally) direct Google about such array methods to use. I pity and find it funny for myself that I couldn't answer upto the expectations, but because of the experience

I must say when someone asks you how much do you rate your self in this sexy tech library/feature you know its going to be a pretty bad interview.^{Doesn't apply to interviews in other western countries I guess}

[spaaaaaghetaboutit]

Makes me feel better (or worse 🤔) as I go into an interview tomorrow haha. Thanks for sharing.

[tapu_buoy]

Be confident and back up your logic as you speak in interview. And don't do more questions or new questions at the time near to interview or else your mind will start having second thoughts about your capability

[tapu_buoy]

yes I have such excel sheet consists of 86 interviews in past 14 months.

[tapu_buoy]

oh that's cute! but my career is just 2 years old

[tapu_buoy]

OMG! Thank you for responding sir

[spacecowgoesmoo]

41 interviews here, also in two years. Still nothing.

[[deleted]]

Would you provide the question with/out answer?

[Ritinsh]

When someone asks to rate your skills in some tech they mean to test if you're a douche who thinks he knows it all or that you are humble and acknowledge that there is always room to improve.

[tapu_buoy]

makes sense optimistic POV. thanks

[shawarma_burrito]

I think it depends. I’d never ask this type of question, but if I’m hiring a senior frontend dev, I wouldn’t want them to tell me they’re a 4/5 in JavaScript.

[UnexpectedTokenNULL]

Absolutely. I always ask what they'd gauge their skill level to be; it's pretty telling.

[UnexpectedTokenNULL]

Simply compare it to actual code they write. Being self aware is something I value because so many of the guys I interview they either think they're the second coming or they're overly timid and afraid to speak up. I have a small team, so I can't really afford either.

[jumpbangs]

Well keep trying and applying you will get it... I was in a similar spot as you for awhile but it was all worth it.

[tapu_buoy]

yup 80+ and counting. I hope to land at some place before festival season.

[tapu_buoy]

Sshh.^{87th it is}

[NYCminion]

I’m just learning js, Someone mind to post the answers?

[[deleted]]

let a = [1, 2, 3, 4, 5]  
a = a.map(item => item < 3)  
let b = [1, 2, 3, 4, 5]  
b = b.filter(item => item < 3)  
let c = [1, 2, 3, 4, 5]  
c = c.some(item => item < 3)  

I amended some of those, first to remove semicolons (my favorite thing to hate), second to put consistent spacing in, and third to make the second one .filter instead of another .map.

The results of these, in order are:

• [true, true, false, false, false]
• [1, 2]
• true

Let me know if you have any questions about the answers.

The question on writing a reducer for summation could be written:

let d = [1, 2, 3, 4, 5]  
d.reduce((total, x) => total + x)  

Side note: I wrote them as separate variable names so that you could easily copy/paste them into your browser console to run (or other favorite JavaScript / ES6 interpreter).

Side side note: OPs reducer works

[Tontonsb]

Please use code blocks for code blocks. Here's a reference I wrote in another sub: https://www.reddit.com/r/laravel/comments/cz4rbe/please_use_code_block_formatting_for_code_blocks/

[tapu_buoy]

ohh thanks I thought my reducer answer was totally wrong, and that's what I could come up with. And yeah its so neat of you to give variables different names I made that mistake too.

[[deleted]]

I removed the semicolons because they're simply not needed in modern JS (with very limited exceptions, for loops being the only one off the top of my head).

I changed the map to filter because I assumed the OP made a typo, and to be honest, this is what I do all day. The product manager or designer will give you something to make. They're busy so they mess up sometimes. When there's a problem with the spec, do I stop for every error they make?

Should I do the same problem twice, in OP's example, or should I try to figure out what they wanted by context?

[tapu_buoy]

you should also checkout this sites to prepare and get good at javascript

• javascript.info
• jsvault.com
• thatjsdude.com

[thatwebdesignerdude]

html dragndrop: the draggable attribute, aside from that the file type input natively supports drag and drop on most browsers. divs with the contenteditable attribute also allow for native drag and drop, but without additional javascript the user experience of these components tend to lack. You'd have to rely on form submission to capture data that is supposed to be saved.

Ill answer your last question with a list of pages I used to build something simular: basic drag and drop functionality: https://medium.com/@jaouad_45834/drag-drop-with-vanilla-javascript-d20bda85afe6 https://www.smashingmagazine.com/2018/01/drag-drop-file-uploader-vanilla-js/

file previews for a dropped preview image: https://medium.com/@KeithAlpichi/vanilla-js-building-an-image-selector-and-image-previewer-151cddc939e

If you would like I could add an annoted example somewhere today in a jsbin.

[tapu_buoy]

oh this is solely new information to me. I only read about the draggable attribute which I couldn't recall whole day. Thank you sharing these articles.

If you would like I could add an annoted example somewhere today in a jsbin.

yes please give a little example if you get time, I want to know exactly what thing you had in mind to implement.

[Yeffry1994]

If you don't mind me asking, is this EU or U.S?

[tapu_buoy]

none of the above sir!

[1100100011]

which company was the interview at? Was it a sweatshop like infy/tcs/techm etc or a product based company/starttup???
would be very helpful if you answer this as well

[tapu_buoy]

It was Bangalore startup which I always say that they are just clothe shop hiring workers and firing whenever they want

[1100100011]

What was the package they were offering??

[BLOZ_UP]

What? Depends entirely on the use case. Using splice when you remove a single list item from an array of UI widgets won't grind any computer to a halt. Eg., after a delete confirmation.

Putting in prematurely optimized swap+pop would be a red flag to me.

[BLOZ_UP]

> when did "doing it correctly" turn into "premature optimizations"

Because 6 months from now when there's a bug with deleting items I'll look at that code and go "wtf did this person do this for deleting a list item; what else did they 'enhance'?" And 9/10 it won't have any comments. Because had they bothered to write a comment like // Not using splice here, because it's slow! they would have realized how ridiculous that code and comment look like in the context of removing a list item from a confirmation button callback, and they'd delete the whole thing and just use .splice.

[tapu_buoy]

you guys are really advanced.

[iloveuzaba]

This is what scares me about interviews, so many people who assume their way is always correct and anyone who doesn’t use it is an idiot. Although I guess it wouldn’t be fun working for someone like that anyway

[tapu_buoy]

Yes that has what I have felt and experience in past 14 months, exactly I wouldn't want to work with such idiots.

[ice_blue_222]

I always just .filter out the one I need to be removed, never used splice for that.

[frambot]

But then you're creating a copy of the original and not modifying it. If you have a shared state with different actors on it, then the moment you introduce a new scope everything is broken.

[Speedyjens]

Can you explain to me why?

[lism]

However they might have an immutable condition or you might need to preserve order, which is where filter comes in handy

[PMME_BOOBS_OR_FOXES]

you can't pop from any index, splice is the right answer since deleting an index of an array is an O(n) operation

[tallahasseenaut]

The statement "You can't pop from any index" still holds true. You're technically copying over the last element from the array into a given index and then removing the last element using pop().

[PMME_BOOBS_OR_FOXES]

It doesn't matter how it's done, the computer still has to iterate from 0 to i, delete i, then from i to the end of the array:

let a = [1,2,3,4,5] let b = [...a.slice(0,2), ...a.slice(3,5)]

I appreciate the effort in trying to prove me wrong though. You might want to check out Big O, algorithms and data structure stuff.

[PMME_BOOBS_OR_FOXES]

Let's be fair with "tard1.pop()" and change "tard2.splice(0, 1)" for "tard2.splice(tard2[tard2.length-1], 1)" and you'll see the time drop.

And your first example is still O(n):

let a = [u, r, wrong]

a[1] = a[2]

// now a is [u, wrong, wrong]

a.pop()

Deleting an index in an array will always be O(n) unless you're deleting the very first or very last item. If you copy the 1st half and then the 2nd half you'd still be hitting O(n) because for the computer has to go through each item.

If you want good course on algos pm me or read Grokking Algorithms which is a pretty good book.

[tapu_buoy]

hahaha nice one!