“Everything is undefined until you define it” -Kyle, 2021

Another big difference is that in an arithmetic operation, null essentially behaves like 0 while undefined will make the result NaN. 1 + null === 1; 1 * null === 0; 1 + undefined; // NaN

You can explain that pretty easily with a JSON file. Where if you do: *JSON.stringify({foo: undefined})* // outputs "{}" but if do this: *JSON.stringify({foo: null})* //outputs '{"foo": null}' This perfectly describes the behavior of null & undefined simply

well I hope those who ask this question at a job interview understands the difference themselves lol

Currently, I am binge-watching your Javascript videos like this and yeah, I have learned many simple things which were tricky to understand. Thank you so much!!

One gotcha is with Default Function Parameters. Null would not get the default value, but undefined will. function log(a = 'hi') { console.log(a) } const u = undefined log(u) // 'hi' const n = null log(n) // null

I use null as a third value to the booleans apart from true and false. Assigning a null value to a boolean in my book means, we checked but couldn't be sure if it was true or false. While undefined variable could mean we didn't bother checking anything in the first place. It's a handy convention.

This is a basic concept, but many people are still confusing about it. Thank you for explaining in a clear and easy way to understand.

JSON doesn't have the "undefined" value, so JSON.stringify({a: undefined}) will result in an empty object, not the case with null tho. In addition ({a: undefined}).hasOwnProperty("a") will return true AND [undefined].length will return 1. So in JS there's even a difference between a value that's not defined and a value that's defined as undefined. What's even more funny is that JSON.stringify([undefined]) returns "[null]" 😅

What you say makes soooo much sense!! Thanks for the enlightenment!

Day by day wds's video are becoming more funny 😄 I liked the start

Great job at explaining the differences.

😍 dude you are really simplifying the web

Very good explanation!

Hea, i've started learning js, you upload it the in the right time

Anyone who started learning programming with a strongly typed language should know this already. Your hard work didn't go in vain my fellow comrades.

I just assume the difference is that null means there is nothing while undefined means there is a variable or something but there is nothing attached to them or otherwise "empty".

had a lot of trouble trying to understand Objects and Classes and when I finally learned them, then came pointers

Aaand I understand it now. Thanks 😁

"I am naming this dog 'Unnamed'." "Well, now Unnamed is a name." "Oh. Uh..."

Can you do a course on micro-frontend ?

Another key difference is if you have any key with the value of undefined in an object and you stringify it it will drop the key entirely where as null would just stay as null.

thx again for this video

I find it hard to use Null in my project, because I use guard clauses and use a lot of if(value ==== undefined) return I don't use if(!value) because sometimes it can be a boolean and false will trigger the guard clause.

Great Video! While I don't disagree with your theory that undefined is the default value and null is something that would be an explicit return value, if you look at the array function 'find' (developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/find) you'll see that if the function can't find anything, it'll return undefined

You read my mind, I just was wondering this

I think, as a general rule, if you feel that you need to set or check for undefined, you should rethink your application logic first.

Like your explainers videos

While the semantics totally makes sense, in reality you rarely need to know if the variable has been defined with no value or if the variable has NOT been defined at all. What you really need to know in practice is if the variable or property has a value or not. Given this concept, using `null` has huge downsides: - you introduce a third typing to your variables => a lot more code to validate (ex: string | undefined | null) - you're actually hinting that you made sure to actually define a variable with no value, meaning I should check if there was a reason for that => I'm gonna waste a huge amount of time chasing ghosts because you couldn't be bothered to tell me explicitly that initializing the variable had no meaning beside your own personal preferences `null` is for a very very specific case: you want to track that the variable exists AND that you specifically set it to no value. This will actually happen maybe 10 times in your entire JS/TS career. My advice is to stop over-complicate things and just use `undefined`. It will simplify testing conditions everywhere. And a bit off-topic but related, try as much as possible to define your data with as less typings as possible. [ Examples ] `string | undefined` is much simper at every level than `string | undefined | null`. Not to mention `string | null` would be an atrocity because it's pretty sure at some point a property in an object would be undefined so it will eventually turn to `string | undefined | null` and you'll be back to the huge pile of problems. `boolean` with a default value is always better than `boolean | undefined`. Pick a default value and deal with it at one place instead of having to test the typings at every single condition throughout your code. Same with `Array` or `[ ]`. Never use `undefined`, always use an empty array instead. You'll deal with the problem once at initialization instead of having to test if the array is undefined everytime you want to use the data. It's always better to deal with the problem at the source than patching everywhere down the line...

When my console logs 'x is undefined' it usually means there's a typo in my code.

How about for the .match() function? If no matches are located, null is returned natively. Wonder if there are any others.

You can mention about NaN constant that it is equal to nothing in javascript, even itself. Javascript crazy and i love it.

Damn JS conditionals. Most confusing is that primitive types can be null. True, undefined is unasigned variable or the variable defined as an abstract being in a code text like a comment. Since JS is a descendant of Java and Java is a descendant of C language, the null in JS must work similarly as in C language. So null, in comparison to undefined, is a defined by compiler or interpreter variable which points to a non mapped address. Sometime it's expressed as the integer value 0 converted to type void. It explains the next JS conditionals: 1 + null === 1 and 1 / null === Infinity. For ref types, null represents a pointer address in the stack memory which don't point to any object or array address in the heap memory. I know, my arguments are rough.

hi there, do you have full HTML and CSS course for beginners? i cant find in your playlists, i would love you have it because narration is really simple and easy to understand

I think the easiest way to cope with this is to never say undefined in your code. but maybe there are interesting use cases idk

well explained

So basically null itself is a value that defines that the variable it is assigned to have no value? On the other hand undefined means that no value is yet assigned to the variable?

So good tutorial

=== is mostly much faster than == .. so I always use === .. When I compare variables that are not of the same type, I normalize them before I compare them. Triple Equal is, in my opinion, a much cleaner way and faster too.

so why do map operations return undefined when they can't find stuff?

The guitar 🎸 in the corner looks amazing 💯❤️🔥

Is setting a variable with a big object or big array to NULL in the hopes of garbage collection an antipattern?

Please make video on TypeORM with node.js..!😌

i just want that haircut tutorial

Most of the time I use this topic to check if DOM Elements exist or not: if (typeof DOMElement != "undefined" && DOMElement != null) {doSomething} What do you think of that? Good or bad use?

And if you get "Nothing" instead of null or undefined, then the *Update* on this StackOverflow post is the solution: stackoverflow.com/questions/7568471/pass-nothing-from-javascript-to-vbscript-in-ie9

I hate having both null and undefined as the 'empty' value, and I find little use with the semantic difference. It's even worse that you can set object properties to undefined, which breaks the semantic difference and isn't compatible with JSON 😒

Defining something as undefined seems really awkward. 🤣😅

null is a blank int value that the systems identifies as null but returns as zero. undefined is the result of a blank int value as zero and using it in a divisionary equation, returning back undefined (can't divide by zero). null can be used as a placeholder/trade value for processing whilst undefined is the definition of a garbage output value - whose only objective is to signal to the programmer (or code, if accounted for) that you created some bullshit it can't use any further.

A more interesting topic would be error handling, like when is it reasonable to throw errors, and when should you simply return silently out of functions.

Tankyou! please make clone of jsonplaceholder locally. it will help deep understanding of nodejs

Just watching this lecture from kyle Simpsons, And another Kyle uploaded this video 😹

you've really simplified this one...

My best advice for learning this shit be honest with yourself. If something is not clear as day figure it out dig. It's just bits and pieces here and there. Good luck to all only danger is giving up.

This is the first that I really hate about Javascript. Why not just nil as in other languages. My way to work with them is everywhere use nulls and avoid undefineds completely. In this case everything is looking the same and is just like in other languages

We need a hair care tutorial

You have to define the variable as null to make it null.

Are you using null and undefined wrongly? Are you wrongly using null and undefined? :D Nice video by the way.

React content needed 🙏🙏🙏🙏

FINALLY I UNDERSTAND WTFF !!!

Me who have already been using js for years asking to my self, am i doing it right lol

So the distinction is useful for debugging but ONLY if people recognize that and never define something as undefined? Super.

soon I'm starting JavaScript fundamentals your view count in old videos is going to increase

Well is null===not defined?

Instead of using null and making the distinction between the two that isn't enforced by the language and will cause confusion, it's better to never use null and only use undefined. if you see null in your codebase that is a code smell. listen to what douglas crockford has to say about null to learn more.

Can you make a video on lit-html?

I learned this in sixth grade.

BTW 'undefine' a variable is usually less performant than initialize a new variable. Re-use variables is not a thing in JS (unless you know what you are doing)

Null is bad enough that people nowadays don't use it. Javascript: introduce undefined

1:41 don't you mean triple equals?

Why is equal == not = as basic maths one = means equal 🤯❔

If a variable or object has no value which equals null...then why leave it in the code i can understand having an undefined object because it could be useful at a later time but defining something as null makes no sense to...I am definitely a novice

I lose my job as trainee software engineer because don't know this concept

if(webSkills == null || webSkills=indefined) { simplify("web", "Kylie"); }

simple, one is 𝚗𝚞𝚕𝚕 and the other is 𝚞𝚗𝚍𝚎𝚏𝚒𝚗𝚎𝚍

A distinction without a difference. it's better to never use null and mark it as a code smell that needs to be cleaned up. listen to what the inventor of JSON has to say about null.

58th

More vanilla js

I can guess it. "undefined" means that the variable is undefined. "null" means that the variable doesn't have a value.

Null means a dev wrote null.

9th comment!

Do a javascript Tutorial...

JS hates logic

Why am I pinned?

Undefined = variable doen't exist Null = varibale exist but does'nt have any value

undefined === void 69

Undefined just seems like waste of time coding that, I am not a fan of computers languages that has things like undefined but they don't actually do anything at all other then labeling something.