Top Tricky JavaScript Interview Questions and Answers 

Thanks, I was reading the comments for this.

Yes, you are right, because the callback function does not return boolean value! It has to return an Integer value (negative, zero or positive). For example, if you want to sort a number's array, you have to write down the callback function something like that : [2, 3, 43, 467, 56, 8].sort((elt1, elt2) => {return elt1 < elt2 ? -1 : (elt1 === elt2 ? 0 : 1)}); // ascending way Output => [2, 3, 8, 43, 56, 467] [2, 3, 43, 467, 56, 8].sort((elt1, elt2) => {return elt1 < elt2 ? 1 : (elt1 === elt2 ? 0 : -1)}); // ascending way Output => [467, 56, 43, 8, 3, 2]

It works in Gecko...I mean firefox's engine...Doesn't work in V8...i.e. Chrome, Nodejs would give unexpected output

Also worth mentioning. You can turn it into a ternary statement using the ? : Syntax, like a < b ? 1 : -1 Then it will return the proper sorting (least to greatest). Or change the above to > sign for same thing but will sort greatest to least. If they are equal then not sure what will happen though because it should be 0 in the case.

try a-b instead of a>b

It is right, good explanation!

@@alreadytakenindeed even if my explanation sounds like a true, you shouldn't believe. It was just my opinion.

Well i guess u r half correct, NaN is non-primitive object and 2 non primitive objects arent equal to each other because they are stored at a different memory heap...

I also bumped into this issue. (a-b) worked but (a

Exactly, and for descending order you would write x.sort((a, b) => b - a);

@@2dabang V8 doesn't support that, I guess, because Node also doesn't support a > b

Yes, I agree. but sometimes people ask such questions and its unfortunate.

Yes, interviewer ask me to solve sum(1)(2)(3) //ans =6.. im really confused after this ques they ask me easy ques but could not answer it because of 1st ques

var i = 0; function sum(n) { i+=n; return sum; } sum(1)(2)(3)(6); console.log(i); I learned from TechSith only. Function chaining.

Sure interviewer asks you these questions, it's really a great video.

Interviewers are asking these questions just to see how you could understand JS. It won't be major part of the interview and they expect you to answer them less than 5 min.

That is the right answer. :)

is there a point to memorizing this type of NaN trivial apart from this interviews. i mean one can always look it up in real life scenarios, no?

techsith hello sir .. can I have your email or contact number.. wanted to talk with you. Please let me know

But isNan(Nan) will be true; isNan('hello') will be true Number.isNan('hello;) will be false. JS is killing me)

Yes, you are right, because the callback function does not return boolean value! It has to return an Integer value (negative, zero or positive). For example, if you want to sort a number's array, you have to write down the callback function something like that : [2, 3, 43, 467, 56, 8].sort((elt1, elt2) => {return elt1 < elt2 ? -1 : (elt1 === elt2 ? 0 : 1)}); // ascending way Output => [2, 3, 8, 43, 56, 467] [2, 3, 43, 467, 56, 8].sort((elt1, elt2) => {return elt1 < elt2 ? 1 : (elt1 === elt2 ? 0 : -1)}); // ascending way Output => [467, 56, 43, 8, 3, 2]

i was doing a project work and came across this issue related to 18 digit number

Easier this way... p.sort((a,b)=> {return a - b;}) Minus sign implicitly coerce them to Number;

yes because its JavaScript :) Basically it try to convert array to string.

Thanks for watching harsh!

I am glad its fun for you, I will make some more. :)

Agreed... The first few questions were valid, then he went off the rails.... GL2U

It’s just a question so to challenge your understand of how es6 gets compiled. It’s one thing to “know that” the behavior of an operation returns an output, but it’s best practice to “know how”, epistemologically speaking. These challenges are just a glimpse into how powerful js can get. Sure, you will not see code written as such because it doesn’t follow the object-oriented principal of being semantic as possible.

@@treyrader OK, you seem like quite a learned individual, and I think I understand your point about OO semantics, but I would argue that JavaScript's OO epistemology -- the actual overarching theme of this video -- is actually "synthetical sugar." I believe you may be referring to Typescript, which as you may know, is a superset of JS. Please correct me if I'm mistaken.

@@Alexanderthenotsobad Hey man, sorry for the late reply as I am just now seeing the notification. I think you are correct that perhaps I was referring to typescript, albeit inadvertently. In truth, my knowledge of web concepts and of JS is, comparativelys peaking, pretty far from vast. This explains why I am on youtube watching tutorials on it as well as why I had to look up the concept of "Typescript.". All that I was trying to express though in my prev comment is that the questions prompted in this mock interview are just a tool for the person conducting the interveiw to assess your ability to problem solve. It makes sense to me that the questions in the end of the interview would seem almost irrevelant and entirely unorthodox to the convention of standard coding so to ensure that they aren't rotely memorized. Were the interviewee to get these correct, surely it'll exceed the expectations of the interveiw and thus ensure that he or she is a spectacular candidate. Cheers!

Yes, you are right, because the callback function does not return boolean value! It has to return an Integer value (negative, zero or positive). For example, if you want to sort a number's array, you have to write down the callback function something like that : [2, 3, 43, 467, 56, 8].sort((elt1, elt2) => {return elt1 < elt2 ? -1 : (elt1 === elt2 ? 0 : 1)}); // ascending way Output => [2, 3, 8, 43, 56, 467] [2, 3, 43, 467, 56, 8].sort((elt1, elt2) => {return elt1 < elt2 ? 1 : (elt1 === elt2 ? 0 : -1)}); // ascending way Output => [467, 56, 43, 8, 3, 2]

Correct!

Thank you :)

You got it. Thanks for the response.

Thanks for the like:)

Thanks for watching venkatesh.

Welcome

You guessed it right. it is false . that is becase NaN compares unequal (via ==, !=, ===, and !==) to any other value -- including to another NaN value.

techsith this was fun, you should consider putting out one trick question or brain teaser every week

Thanks for the first comment:)

const aa = () => 1; It has to be explicitly declared to use as a callback.

@@flysports3856 var res= aa; function test(cb){ if(typeof cb === 'function'){ let output = cb(); console.log(output); } } test(bb); This might help

I think we can do like this function aa(b) { console.log('sum is : ' + b); } function bb(a, b, cc) { let x = a + b; cc(x); } bb(1, 2, aa);

@@swetharedddysh Hi thank you so much . Your solution works well.

For numbers you need to use a-b

Here it is: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-pFEdFfB2ewE.html

There was i / i not i / 1.

Nan is an exception, you will get false

Thank you

If you watch the video there is another line which is missing here. if you add that you will get expected result.

X.indexOf(10000). Wrong brackets

learn latest version of JavaScript don't try to learn old deprecated stuff and then pick a framework like react.

Here it is: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-pFEdFfB2ewE.html

which particular one?

I was going to upload that video with this video but go busy. I will upload this weekend.

What abou this ? var sampleArry = [1, 2, 3, { a: 4, b: 5 }, 6, 7, 8, [9, 10]]; sampleArry[7].map(res => { sampleArry.push(res); }); sampleArry.splice(7, 1); let obj = Object.values(sampleArry[3]); sampleArry.splice(3, 1); sampleArry.push(...obj); console.log(sampleArry.sort((a, b) => a - b));

const arr = [[0, 1], 33, {a:4}, [2, 3], [4, 5]]; const newArr = arr.reduce((acc, b) => { if(Object.values(b).length) b = Object.values(b); return acc.concat(b);; }, []); console.log(newArr);

indeed :)

That is a correct syntax for the callback. a-b is correct.

​@@Techsithtube I made a fiddle in which I console log the example you used in this video that isn't working for me. jsfiddle.net/2yr69pn7/ I'm really confused why the minus sign is doing the sort correctly but the less/greater than sign isn't. Thank you for the instant reply! That caught me off guard haha :D

Its basically how the sort is implemented in javaScript other languages a>b makes sense but javaScript decided to go this way.

Because program stopped running after it gets an error from console.log(a)

@@kannu755 Thank you ...

what did you get?

Should be return a - b

JS is confusing for programmes from other languages. First of all its nonblocking and second of all it has lots of weird things that you can still use it but you shouldn't. I would suggest to learn only latest JavaScript .

As i said in the video after 16 numbers its all wierdness so you should not have integers that are longer than that.

techsith, I am still having doubt. Why it wasn't like 55555555555555560 with 5's similar to 44444444444444450 with 4's. I know, after 16 digits, it's all absurd but with others, we see that 16th digit increments and further digits truncates to 0s. Please clear me also on this. Anyways, I liked this video a lot. Keep going!

THere is a MIN_VALUE in javaScript that is the smallest possible number. and adding one to it changes that number slightly. removing from the smallest number should make it a 0 same with multiplication. however, dividing the same number should give you one.

Because it truncates.

Lol. Math is very important to pass as an engineer.

hmm, I think logic is more important but I can be wrong, good video btw. made a lots of people salty XD

Yes. it would be false. the only way to check NaN is isNaN() function.

Yes, That is right!