Javascript闭包是否始终保留范围变量？

Question

I understand that code in closure can access variables & methods & arguments up the scope chain, but what happens if it doesn't use any of them ? do those variables still retained ?

Consider this case :

function f(){

  var a=[];
  for(var i=0;i<1000000;i++) a.push({});

  return function(){
     alert('Hi');
  };

}

var x = f();

Does variable a retained in memory even though the closure does not use it ?

Thanks

UPDATE: Seems there's no answer about 'trivial' closures. So is it fair to assume that each and every closure ( even if it does nothing at all ) may retain in memory all the methods up the scope chain including their arguments , variables and inner functions ( until the closure is garbage collected )?

Also, about the 'possibly duplicate' question about node.js - to my knowledge node.js runs only on a dedicated environment that based on google's v8 JS engine. Here I'm talking about web-apps that will run in any modern browser ( in most cases )

Answer 1

When the interpreter chooses to free the memory it occupied is an implementation detail - there is no single javascript interpreter.

Note that it's not always possible for the interpreter to know the variable is unused:

function f() {
    var a = 123

    return function(x) {
        alert(eval(x));  // if there's an eval, we have to hold onto all local variables
    };

}

f()('a')

---

Experimenting in the chrome console

var e = eval

var f = function(){
    var a = 123;
    
    return function() {
        return eval('a');
    };
};

var g = function(){
    var a = 123;

    return function() {
        return e('a');
    };
};


f()()  // 123
g()()  // ReferenceError

It appears that V8 is making optimizations based on the present of eval