1) "var" is function-scoped, whereas "let" is block-scoped. 2) Using "var" attaches the variable to the window, whereas "let" prevents it.

Mosh is the best teacher, calm and friendly voice, perfect speed and flow of speach. There are only a few software teacher, who increases my mood when following the tutorials and he is one of them!

Finally, I understood the difference between var and let. Great video.

Short and to the point explanation! Thank you very much! I'm learning JS right now 😁

You didn't explain what const does.

CONST is a 'variable' that cannot be changed. It is a CONSTant. This is useful as a control so that you don't inadvertently make a change to a variable. You can define all your variables as CONST and change them as needed if you find you do need to update them.

I bought his js course recently. I’ve tried several courses and can honestly say this is one of the best. His explanations are very clear, for the most part. I love his explanations and upbeat attitude. I just wish there was some way to ask questions. There is no area for that on teachable, as there is on Udemy.

Mosh jan, you should add WHY bloating the "window" let say or other objects with variables and functions is bad. watching your video, a novice would think, "well, why would having access to data outside of a scope bad?!", which is a valid and good question. Otherwise, a very nice video, thanks :)

ALOT of "javascript gurus" have all made 5-minute videos on the history and distinction between var and const and let, then NEVER actually DEFINED any of these terms, but instead launched into some over-caffeinated babble of code examples where utterly NOTHING was explained, but they're oh-so-proud of themselves. YOU alone (so far) took the time to actually DEFINE these terms first: "const", "var", "let" and even "function" and "block" AND even "function-scoped" and "block-scoped". Then you examples were simple enough to make your target audience - PEOPLE NEW TO JAVASCRIPT WHO DON'T UNDERSTAND SOME OF THE CONCEPTS - actually understand the distinction between "function-scoped" and "block-scoped" variables. Well done you - you just EARNED yourself another subscriber. Cheers, -Mark Vogt in North Aurora IL (USA)

I know it is VERY confusing because var and let are EXTREMELY THE SAME But they are a difference That for example, var x="john" ; x is defined in your whole code, not only in this block And you may change it depends on how you want and you can't use x in other functions let x="John" Defines x only in your code block And you can only make it work by putting the method for example console.log inside of the curly braces of the function they're in it

Variables in Python also have the same scope as var in JS. I never thought of it as a real problem but I agree that it can sometimes result in bugs.

let variables cannot be read/written until they have been fully initialized, which happens when they are declared (if no initial value is specified on declaration, the variable is initialized with a value of undefined). This differs from var variables, which will return a value of undefined if they are accessed before they are declared.

I was searching everywhere to understand the difference and finally found this video. Really helpful! Thanks for making this video. :D

The best explanation of let and var keyword so far, Thanks

Very clear explanation, but I don't understand the why var is a problem at 3:13

A great and simple explanation of var vs. let. Thank you Mosh.

Great tutorial, I've more understand with it. Thank you

For some reason var apple = 'apple'; console.log(window.apple) throws undefined, like It is not attaching apple to the window object..

What's the concern with var if you really need it althrough out the function scope?

After watching this and searching a lil bit, i think it's wrong to try to use let for everything, since var is function-scoped and let it's block-scoped so you should use both and not only one, like two for inside of one you need to know the two loops indexs and using let you'll not have this information and not even any result outside of them which is bad since we may need the result of others scope functions inside others functions, we don't have thoose "problems" using C# but i don't agree with using let in every situation, it may give even more bugs than just using var which is like most of the languages work which was what a lot of people were saying about let, let should be only used when you know that you'll not need that variable anymore outside of that situation, btw amazing tutorial, js it's preety cool. global variables and function-scoped variables;

i was not good at all in the variables but now im proud of myself thank MR mosh

I came here to learn about const. I left without that knowledge.

The reference point to the Window object is quite significant. It may cause leaks and overrides. Good thing to know.

const is also block-scoped, but It can't be reassigned. You can modify them but can't reassign them.

so should we use them in some cases or avoid using them forever

Packed with information, but short and concise. great video

I'm at complete beginner level, been learning only for a couple hours. So I don't know enough to know why you would even want to have variables be block scoped instead of having all variables be global and each of them having a different name. To me seems like the latter would be easier to work with so I can remember what each variable does better but I since i'm so new I will just trust you.

helpful information thank you

let sayHi =function() { console.log('hi');}

Clear and straight to the point

Seeing the examples it's all clear... We must NEVER use var. Amazing how easy you make it look

Thanks for this video. Finally understood the difference between var and let

3:35 I dont know why is that a problem. I mean I know when the codes get complex it will be hard to manage the window stuff but sometimes if it's neccesary to use it, it can be used in my opinion

The best explanation ever! Thank you very much!

Finally I understood the differance thanks Mosh !

Sir can you please make a video on Closures in JS..

Hi sir,I have a doubt when using const keyword value will not change but when I use like this value is changing for 'const' keyword. code is: const x = { name: "scott"}; x.name = "john"; console.log(x); Result:john. Why const is printing john instead of scott. Can you please give me reason.

What a wonderful way to explain. loved it.

first time watching your video, great explanation! Thank you for your help!

Super helpful you explained it very well.

This was an indepth ans to the question. Thanks Mosh ❤❤

Mosh, You are the best man

How do I get this view with VSCode and live output to Chrome console? Is this simply tied to an HTML file that's not being shown?

Hi Mosh. If var attaches variables to the window/global object where are those declared with let/const attached to if they're not declared inside a block? Thanks, great videos btw

The question is where do those variables declared using let or const go?? Somewhere in the memory?

Very good and clear explaination my friend!!

Hi Sir!! You said that the variables declared with let keyword is not attached to window object, then where is is stored ? If it is stored is script scope, can you explain the script scope as global scope?

What about constant?

Thank you so much, that was crystal clear.

what if i want to declarate global variable inside of function?

So for, for loops, I should still use var?

Really good tutorials!! You should make some courses on udemy! Thank you very much

Hi Mosh, what is the name of your VSCode theme?

why we even have var then? What's their purpose/adventage of it if any

Great video, thank you. So if I declare a variable using let in the global scope, does that have the same scope as the window object?

This video was well done. Mosh, you tha man

Awesome. I understood very well.

Great video but it would have been nice to have it numbered since it appears to be part of a series.

Great content loko. I subscribed by the 3rd video.

You spoke at 5:37 about function encapsulation/modules and another video, that will explain this concept. I didn't find this video? Can you please link it or i have to buy the full course first? Thanks in advance

I hate to sound stupid but why if the loop terminates at i < 5 is the sixth var 5 and not 4? I thought the loop terminate. Does this mean the i++ is the last bit of information at the end of the loop however it wouldn't display it on the console? (meaning the value of i at 5 is assigned but not printed?

love it SIr thank you

Hi Mosh please make tutorial on spring boot and especially spring security .It will be very useful for lots of people , especially of you are doing :)

Thanks Mosh!

thanks :D quick and well explained!

Marvelous bro marvelous

You are awesome Mosh!!!

What's the difference between using “let” and “var”?

I have a question. I am a UI dev for a web based application company. Now majority of our clients are using very old machines and old browsers which were not updated. If I start converting my JS code from ES5 to ES6, will it cause issues running in those old computers? What is the solution?

Whats your color theme in VS Code ??

nice explanation ..

thanks a lot

I don't have time to watch all the other lectures or watch till I find what he said so can someone tell me how to prevent a 'function' from being added into window? Thanks in advance

Great video

What theme is he using?

for(var i=1;i

I have to commend you. I have searched for the use of the Var or Let keyword. Currently am ongoing a course but got curious as to why in my course there is only Let and no use of Var nor Conts.

how to enable window and global object in node environment?

Where can I find more info about the function encapsulation? Now I'm curious

god tier explanation thank you, sm

Thank you!

In addition to everything mentioned in this video, let has reassignment protection. What I mean by this is the following: If you declare a variable: var test = 'test'; and later have: var test = 'new test'; then the variable test will be reassigned, sometimes without your knowledge. with let, this does not happen. If you declare: let test = 'test'; then later: let test = 'new test'; You'll hit a error/warning that test has already been declared. Unlike a const however, it can still be reassigned the 'normal' way, which is much more intentional: test = 'new test'; because you are not using let before the name of the variable, it is clear that you know the variable already exists, and you are reassigning it. This protection helps prevent accidental reassigning of a variable you already declared but then may have forgotten about, and reduces debugging. Yet another reason to use let instead of var! note - const cannot be reassigned at all, even using the 'deliberate' way shown above, it is not a variable, but a constant. It does not change.

Hi, what color theme are you using for VSCode? Thanks

well explained

Const??

So using let is more secure? I’m curious, you would only want to limit the variables scope to only where it will be used/accessed?

THANKS!

Mosh is the best!!!

Love You bro

thx

Please put this course in udemy. I love your videos. You're the best

what is his apps ? what name of that apps? i

const is don't can change.

I think you forgot the constant from your title :)

1:39 "I becomes 5 because 5 is not less than 5" Can someone explain this?

Thanks a lot

Weird. Game maker uses var for local variables, it's the opposite in js.

what if you just used test = 'color';

But why are there like, MOST of the developers that use var over let?

I still use var