How to understand closures and garbage collection mechanisms?

recently I have read articles about garbage collection mechanism and closures, but I still don"t have a deep understanding of them, and there are some doubts. I hope some bosses can give me an answer

my understanding is that local variables are recycled after the function is executed, while global variables are not recycled until the window closes (because of the life cycle of global variables? )

so will the function declaration be recycled? Recycle only variables? The following example:

function a(){
    var i = 1;
    function b(){
        return i
    }
    return b
}
var x = a();
x()

after executing x (), the function an and the internal variables I and b will be recycled?

Another function of

closures is to reside in memory, for example:

for(var i = 0; i< 9; iPP){
    (function(i){
        setTimeout(function(){
            console.log(i)
        },1000)
    })(i)
}

this example is to save the variable I in an anonymous function, so will I be recycled after the function is executed?

Javascript closure garbage-collection-mechanism

Mar.14,2021

memory Management-tag-clear algorithm part

function declaration: the function declaration is the same as the variable, but if the global is still available, it will not be recycled. function fun () {}; fun = {}; then the memory that originally belonged to the function part is reclaimed.
function: x = a () , the last x is the internal function b, and the internal reference I of the function b, then b and I will not be recycled. After the execution of x () , x still maintains the reference to b globally, and b and I will not be recycled.
similarly, after the execution ends, the global I can still be obtained, so the global I will not be destroyed.
- as I understand it, there are two I's here.
- closure exists in the anonymous callback of setTimeout. The reference to the I of the anonymous function (IIFE) is executed immediately in the outer layer. The I of this layer is destroyed after execution. This is the argument I of IIFE;
- another layer of IIFE is not a direct reference to the global I, nor a closure, but a simple parameter transfer. The relationship between the global I and the global I is only two variables with the same value at that time, retaining the value of the outer I at that time.

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