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Where does JavaScript (according to the standard) store closures: heap or stack?
Is there a third explicit place for closures?
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It is created and destroyed every time the function is executed, and it cannot be accessed by any code outside the function.
So. With this in mind, the answer is that variables in a closure are stored in the stack and heap.
A Closure is a combination of a function enclosed with references to its surrounding state (the lexical environment). In JavaScript, closures are created every time a function is created at run time. In other words, a closure is just a fancy name for a function that remembers the external things used inside it.
In the end it is an implementation detail of the runtime. See Phoenix link
As to implementations, for storing local variables after the context is destroyed, the stack-based implementation is not fit any more (because it contradicts the definition of stack-based structure). Therefore in this case closured data of the parent context are saved in the dynamic memory allocation (in the “heap”, i.e. heap-based implementations), with using a garbage collector (GC) and references counting. Such systems are less effective by speed than stack-based systems. However, implementations may always optimize it: at parsing stage to find out, whether free variables are used in function, and depending on this decide — to place the data in the stack or in the “heap”.
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