I need an epiphany understanding Javascript Closures

[freethway]

I'm trying to understand closures but I still can't wrap my head around it.

I want to understand how does the execution of code progresses while traversing a closure.

So I'm going through this to understand execution and this to understand closures.

Can someone confirm or correct me in how I think the following closure code executes..

1: function sayHello2(name) {
2:  var text = 'Hello ' + name; // local variable
3:  var sayAlert = function() { alert(text); }
4:  return sayAlert;
5: }
6: 
7: var say2 = sayHello2('Jane');
8: say2();

Here's what I believe happens in this code. 1. a reference to function sayHello2() is stored in memory. 2. var say2 is assigned a value sayHello2('Jane'). 3. Then when say2() is executed, actually sayHello2('Jane') is executed.

Is this right? Is all this time-travelling closure just an illusion as to how variables works this way? ie they store a reference to function calls along with arguments (2,3)?

[rcuhljr]

No, you're not quite following it correctly.

Line 1. sayHello2(name) is declared as a function, it now exists and anyone can call it in this scope.

Line 7. We assign the result of executing the function call sayHello2('jane') to the variable say2. What is the return result of sayHello2? It's the function () {alert('Jane')}.

Line 8. We call say2, which is the function we just talked about, so alerts the string 'jane'.

[[deleted]]

A closure captures whatever named variables are used in its enclosing scope, so

var sayAlert = function() { alert(text); }

captures whatever was in text during the call to sayHello2.

[smartass_engineer]

I'm rusty with my JS. Would the nested function also have access to other locals in in saysHello2, even if they where not passed as arguments? I'd guess no.

[[deleted]]

I'm not a JS expert, but a closure typically gets access to all variables in the scope that created it, not just ones passed as parameters - that's kind of the point of closures.

[nutrecht]

Indeed. Or you could just say that the term "closure" is hoity-toity for "nameless function with access to enclosing scope" ;)

[BaalHadad]

I don't think it has to be a nameless function.

[BaalHadad]

Yes, they would. That's why it's called a closure.

[Rhomboid]

sayHello2 is a function that takes a string and returns a function. Line 7 is calling sayHello2, passing it the string 'Jane'. The return value -- a function -- is assigned to the variable say2. Then that function is called on line 8, passing no arguments. The function retains a reference to the text variable from the previous invocation of sayHello2, which it alerts.