Javascript lexical scoping closure in a relationship

Learn Closure – The Good Parts of JavaScript and the Web

javascript lexical scoping closure in a relationship

Also, JavaScript has a fairly verbose lambda syntax. . are implemented in JavaScript (not surprising considering its close relationship to This is done via a function, which creates a private scope = closure . in a dynamic context where it should not be called (reading from a closure after a stream is closed, for example). First, although javascript falls under the category of 'dynamic' or 'interpreted' languages it is actually a compiled language. I'm no compiler-guy. I'll remind you all again that in C# the term "scope" has a very we have defined “scope” as being a relationship involving text, so is this kind JavaScript, though a very dynamic language, is actually for the most part . I am also glad that Emacs now supports lexical scoping (and closures) as an opt-in.

We're finally getting to a good part and this is something that you probably don't have experience with. It's something called closure.

JavaScript scope chain tutorial - understanding js scope and scoping rules

It's also called Lexical Scoping or Static Scoping. It's a consequence of functions that can nest and functions that are first class values, and JavaScript has it, and is almost completely right in the way it implements them, and it's maybe the best feature ever put into a programming language. I expect that statement made no sense to you at all and I understand that. So, I'm gonna have to explain this in steps. So, you're familiar with the idea of block scope.

So next year, we'll probably have let statements in most of our systems.

javascript lexical scoping closure in a relationship

And here, we've got two blocks. One inside of the other and the inner block can see its variables, and the variables of the outer block. So, I assume everybody is comfortable with the idea of block scope. We've had that since and it's great. So, we can do the same thing with functions. You can think of a function as simply being a block with a little bit of extra mechanism attached to it, so that you can invoke it in the future.

So we've got the yellow function, which can see a and b and the green function that can only see a.

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Exactly the same relationship and we can represent this relationship as sets. So, this is the set of variables that the outer function can see and this is the set of variables that the inner function can see.

And it's kinda too bad that we call it closure, cuz most people think of closure as meaning something else, like retribution or vengeance.

javascript lexical scoping closure in a relationship

But it's not that kind of closure, but that's what we're calling it. So, we're kind of stuck with that and it seems like a simple idea.

What is lexical scoping?

Just add nested functions, which have what should be an obvious relationship, because of the way that scope works, but it took a long, long time for this idea to get developed. He needed lexical scoping. He needed nested functions and functions, as first class values. And pretty early on, we got functions that would have two out of three, but we didn't get a function that had all three until scheme.

Scheme was an experiment at MIT in an attempt to understand Carl Hewitt's after model in their early 70s. And like all of the really important, significant breakthroughs, the world took no notice of it whatsoever.

You see, every variable is born, lives and dies. The beginning of a scope marks the time the variable is born and the end of the scope marks the time it dies. In the beginning there's only one scope called the program scope or the global scope. Variables created in this scope only die when the program ends. They are called global variables. For example, consider this program it's not JavaScript: Then we created a block scope. Inside this block scope we created a local variable x. Since local variables shadow global variables when we print x we get Back in the global scope when we print x we get 10 the local x is now dead.

Block Scopes and Function Scopes Now there are two main types of scopes in programming - block scopes and function scopes. The scope in the previous example was a block scope. It's just a block of code. Block scopes are immediately executed.

Function scopes on the other hand are templates of block scopes.

programming practices - Why would a program use a closure? - Software Engineering Stack Exchange

As the name suggests a function scope belongs to a function. However, more precisely, it belongs to a function call. Function scopes do not exist until a function is called. That's the reason you get the outputs 4, 10 and 8. JavaScript only has function scopes.

javascript lexical scoping closure in a relationship

It doesn't have block scopes.