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Comment by cqqxo4zV46cp | Hacker News Reader

Yup. I’m hiring for a mid-level FE role right now, and the number of “React developers” that don’t know JS fundamentals is incomprehensible. I’m not talking about anything esoteric. Just the sorts of things that I as someone that’s far from a JS expert considers necessary to work in that space day to day. I’m more and more just taking it as a given now that someone won’t have much if any experience writing CSS by hand. If they do, never in an actual .css file. Always via some CSS in JS something or other. A strange new world out there.

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Give us some examples of JS fundamentals they do not know

Not op but “write hello world to the DOM” and “make an http request” are questions I’ve seen go unanswered many times.

Honestly I can’t remember half the dom manipulation stuff and at one point I did know it quite well. It’s just been 6 years since I worked on an app that wasn’t react.

It’s useless knowledge for most people now. Like knowing assembly.

I wouldn't really consider anything involving the DOM to be a JS fundamental. That's a browser fundamental, and even then, it's like, what do you want? I can use `document.write('hello world')` and replace the entire body. Or append it as a text node with `document.body.append`. Or create an element and add it. This is a pretty silly question and something people should just spend 2 seconds looking up on the rare occasion they need to do it.

I currently work with devs who've done things like create a Map and then assign properties directly instead of using .set and .get.. I'd say that shows a pretty significant lack of fundamentals

I believe Map was released in 2015 as part of ES6 so while not new, it still feels new in some code bases. Some people also confuse it with Array.prototype.map a lot.

People just assume every data structure operates like an array since it is the most commonly used without realizing the underlying object nature of the language. Like the idea of getters and setters coming from OOP paradigm is lost to fresh devs over the last 5 years using the FP paradigm as their primary means of coding in React.

So yeah some of the fundamental are missing but also most of the time this knowledge probably isn't utilized by React FP only devs in their day to day.

"make an http request" as in fetch() would be OK, but doing "classic" XHR in an interview? Hell no, I've got better things to do.

I write this blog a while ago:

https://lolware.net/blog/react-xss-protection-cheat-sheet/

The feedback I got across the board was generally "what even is this code? If you it to work with react why isn't it a hook?"

What does "across the board" mean? You mention that the article scores for newbie Google searches about XSS in React.

I mean, it's correct that people who ask such questions should spend a year doing web dev without React probably (and maybe learn basic programming concepts). But the people who comment to you about that post seem to be self-selected for not knowing much about JS.

People who know their ropes aren't left with any questions by your article :) and probably know about everything it contains already.

Still, feedback from me: good content, especially for beginners!

I would assume array methods (map, filter, reduce), callbacks, hoisting, mutability, etc.

I've interviewed a few people who don't know how some of the array methods work, and those are one of the most important parts of knowing how to write Javascript.

I've reduced my JS interview test to just one question: "What examples of falsy values can you name?".

Anyone working with the language will be inevitably regularly reminded which these are.

The least mentioned is NaN followed up by... false. But I can't blame anyone for forgetting that one, as it's too obvious.

That's one of the worst interview questions I have ever heard.

If its just the one question then sure i agree... but if it was used as a kind of fun icebreaker question, then I can kind of see where it could be used.

But it's just very much asking around https://javascriptwtf.com/ level stuff

Can't agree here.

Especially when you deal with unsanitized data - like from a 3rd party API - you're bound to eventually have each of those cases find their way into your if statements/expressions.

Also, this question works for other languages too, as e.g. NaN can evaluate to True (Python) or have an undefined behaviour but still evaluate to true (C, C++) - it's useful to know what is true and what is false(y) in your language of choice, especially coming from another language.

Thank you for your opinion - it's proven reliable over the last decade.

Since I didnt think such word even exists I googled and apparently there is something called "falsy" in javascript.

To make it worse, there is a "truthy" too.

I guess a technical question. But my eyes.

null, undefined, NaN, false, 0, ''

How did I do?

Don't forget -0.

That's just another name for 0

But a different representation in IEEE 754 floating point. If you were building a JS interpreter it would be important to catch that 0 and -0 are different numbers in memory and to hardware operations.

MDN specifically calls it out.

https://developer.mozilla.org/en-US/docs/Glossary/Falsy

0 === -0

MDN specifically calls it out.

https://developer.mozilla.org/en-US/docs/Glossary/Falsy

Hold on the real nugget here is that apparently document.all is a falsy object. Why in the world would that be the case?!?

I agree! Last time I looked at this page, this was not there.

Perfectly.

You forgot 0n ... I guess you wouldn't pass

Got me there, as I forgot about it, but I also don't expect anyone to always name all of them - as it's just a probe on how broad was the spectrum of errors a person encountered.

Personally I've never had an issue where that would matter, as BigInt is typically used mostly in isolation. Any avenue for errors appears only when types are mixed or used in boolean statements.

If we're being pedantic, you also forgot document.all. Which is in fact an infinite collection of values, because document.all is a different object in every frame.

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