Lifetime of JavaScript variables

Question

What is the lifetime of a variable in JavaScript, declared with "var". I am sure, it is definitely not according to expectation.

<script>
function(){
   var a;
   var fun=function(){
     // a is accessed and modified  
     }
}();


</script>

Here how and when does JavaScript garbage collect the variable a? Since a is a part of the closure of the inner function, it ideally should never get garbage collected, since the inner function fun, may be passed as a reference to an external context. So fun should still be able to access a from the external context.

If my understanding is correct, how does garbage collection happen then, and how does it ensure to have enough memory space, since keeping all variables in memory until the execution of the program might not be tenable ?

This is a great question btw. It points out that the closure itself isn't the only thing that is held in memory until the closure is GC'ed. The entire scope chain of the function is as well. There appears to be some controversy, but some additional thought would seem to indicate that every function declaration in JavaScript is a closure, relative to the global scope. However there is an exception see this answer — Shanimal
– Shanimal, Commented Mar 17, 2016 at 17:15

artemnih · Accepted Answer · 2014-09-30 15:33:25Z

5

The ECMAScript specification does not specify how the garbage collector should work, it only says that if an identifier is reachable (through a direct pointer or a closure), it shouldn't be GCed.

Check out this article about identifier resolution, closures, scope chaining and garbage collection in ECMAScript.

Hope it helps

edited Sep 30, 2014 at 15:33

artemnih

4,2392 gold badges20 silver badges29 bronze badges

answered Apr 22, 2010 at 12:28

Pablo Cabrera

5,8475 gold badges26 silver badges28 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Rolf Over a year ago

Alas, dead link

Jeffery To · Accepted Answer · 2010-04-22 12:58:51Z

1

'a' will not be garbage-collected as long as there are external references to 'fun'. The browser ensures it has enough memory by asking for more memory from the OS.

answered Apr 22, 2010 at 12:58

Jeffery To

12k1 gold badge29 silver badges42 bronze badges

1 Comment

Sergey Orshanskiy Over a year ago

"The browser ensures it has enough memory by asking for more memory from the OS." - lol... fair enough :-)

Collectives™ on Stack Overflow

Lifetime of JavaScript variables

2 Answers 2

1 Comment

1 Comment

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

1 Comment

1 Comment

Your Answer

Sign up or log in

Post as a guest

Linked

Related