So we all know by now how variables are declared in years five and earlier versions of Javascript. But what about ESX What does iOS bring to the table and yes is concerned with scope in terms of variables. Variables are what are called functions scoped and what that means is no matter where you declare your variable inside your function. The topic of scoping by digital marketing agency Mumbai in javascript is important to cover.

 

You always have access to that variable even if you shouldn't. So as an example of that let's read a really simple function here called function. Say hi and as you can imagine this function is just going to say hi and let's say we have a boolean check here. So we'll just have a simple IF statement which is just going to check if something is true.

 

So let's say var should say hi equals true. OK so it should say hi and we can just check if this variable is true or not. Right so it should say hi equals true and technically we don't need to say equals true you could just say if it's high. But anyway if I should say height equals true then we'll declare a variable here. So far my name equals Chris ok cool. And we can then console log high plus you know what let's be consistent we use double quotes everywhere instead of single quotes some places and double quotes other places high space plus my name. OK. No issues here.

 

Nothing wrong going on. Let's invoke the function. Say hi. We'll run it. OK. Hi Chris. That totally works just fine. Now, what about if we tried to access this variable outside the scope of this if statement. Theoretically speaking that shouldn't be possible. The digital marketing agency Mumbai should consider javascript as a main part of the topic. We're not declaring the variable until this block is called the block until this block is invoked. But the way that variables work in. Yes. And in fact, all versions of javascript even need six if you declare a variable. It'll work this way. You do have access to this variable outside of that scope provided you're in the same function.

 

So if I take this out and I move it outside of this block. So you know it let's put some lines in between so we can kind of tell it apart. So this should kind of stand on its own but if I say down here. OK Cancel log. This plus my name and you want my Linter is telling me right off the bat hey this is otoscope and it's totally correct to do so. However, this is valid javascript. This will work so if I clear this and run it again and I'll save it for good measure. Run it. We see that it is working.

 

We have access to a variable where really we probably shouldn't. And as you can imagine this can cause some headaches down the road if you have a really complicated function and it's all you have a bunch of nested if statements for example. And at some point, you need to check that variable and digital marketing agency Mumbai. Or you know you accidentally reassign the variable that could be a real nightmare. Right so if you say for example here my name equals Bob here.

 

We're axing a variable that we shouldn't have yet. Right. It's dependent on should say high. So if we clear it we run it again. It changed to Bob which is not really good. Right so we declare it here it just kind of runs sequentially we declare it and then we reassign it to a new value and we cancel that out and now we are having an unintended consequence.

 

Right because this variable is scoped to the entire function. The show even further how this could be bad. You know if we say should say her true or really say high equals true. Right. So let's test this even deeper. So you know I'll get rid of some of this code here. So here is a VAR my name equals Chris. And then we say if really say hi equals true Leclaire another variable for my last name equals just to make something up. Smith So again this variable even though it's kind of nested deeper inside the if statement. And if your eyes are kind of cross I don't blame you.

 

But even though this variable is declared deeper within this statement I do have access to it within the scope of the function. So here I can reassign it. My last name equals Jones for example. And again my Linter is telling me that hey this is out of scope. But again this is a valid javascript's not going to crash as told by digital marketing agency Mumbai as I can see my last name. It looks like it's still running through all the code here run it. OK let's console log onto a log. Hi Plus my name plus my last name.

 

We don't have any spaces in here but just to demonstrate this. Hi, Chris Jones right. So this is kind of a pain. What if you have tons of nested stuff going on in your function you do have access to the variable outside the scope. Not really an ideal situation. And you know if you try to access a variable outside the scope of a function it's not going to work.

 

So instead of saying Hi Here let's try to access a console log my name. Let's see what happens here. Crear run. Of course, it crashes because my name is not defined at this point in our program. And you know even if you move this down to after invoking the function it's still going to fail. Right because you're trying to access something outside of the scope. So clear run right so error my name is not defined. You know let me save that and run it again.

 

Right so hi Chris Jones this runs and then this line of code runs. And of course, my name is not defined outside of this function. So this tells you a couple of things. First of all, you should really be careful with globally declaring variables and digital marketing agency Mumbai. Just do it at least you know the least amount as possible because if I did declare my name at the very top it's not necessarily anything wrong with that but it should always be careful in terms of scoping your app.

 

Your function should be kind of minimally scoped as possible and on the other hand, you do have to be aware that variables do get scoped to the function. Now that brings us to some E- code finally. So iOS code introduces let. Which is kind of in contrast to var? So let me rewrite some of this using LET instead. And I'm going to get rid of console log down here.

 

So let's say you know let's keep var should say hi should really say high but let's say we make my name into a LET instead of var So we're declaring this now like a variable. And for all intents and purposes acts like a variable with the exception that lead is scoped to the block. Right so recall that this and you know I'll get rid of this.

 

A couple of lines of code here actually kill get rid of my last name like so. So let is scoped to the block and the block is you know this line of code that follows an if statement. So I will not have access to my name outside of this block meaning if I try to run this code it's going to crash. Let's see what happens. Run ever. My name is not defined.

 

Right, so this is going to help us a lot in terms of scoping out our app or our function or whatever it may be. Right. So here we are declaring it if we want to say Consolo my name inside the block that will totally work. So like so clear it will run it totally works right. And you know what. Let's add a space here just for aesthetic reasons plus it's so we can run it and it works.

 

We do not have access to this variable outside of this particular block. Right. So that's really key to understanding when it comes to letting. And that doesn't mean you can't kind of filter it down. If I declared at the top of this function, for example, let And if I wanted to cancel log out one of those, for example, should say hi instead of Hi my name. All right let's see if this works clear it will run it again. True right. So this block is still within the context of this function block. Therefore I do have access down the road but I can't pass anything I declare back up out of the block.