获取Javascript中的闭包变量列表

Question

Are there any ability to get closure variables list (Ok, maybe all scope variables) in JavaScript?

Sample:

function factory(){
    var _secret = "Some secret";
    return function(code){
        // How to get parent function variables names here? 
        // ...
    }
}

var inside = factory();

inside();

Answer 1

Assuming this is for debugging purposes, you can try parsing the function body and evaluating identifiers found:

 function getvars(fn, _eval) { var words = String(fn).replace(/".*?"|'.*?'/g, '').match(/\\b[_A-Za-z]\\w*/g), ret = {} words.forEach(function(w) { try { ret[w] = _eval(w) } catch (e) {}; }); return ret; } function factory() { var _secret = "Some secret"; var _other = "Other secret"; return function(code){ var vars = getvars(factory, _ => eval(_)); return vars; } } vars = factory()(); document.write('<pre>'+JSON.stringify(vars,0,3));

Needless to say, this is an extremely naive way to deal with code, so handle it with care.

Answer 2

There's no comprehensive way to get a list of all variables in scope. You could enumerate over the this object, but that will still only give you a list of the enumerable objects on this , and even at that there will still be things like function arguments that aren't on this .

So no, this cannot be done. Also check out this similar question .

Answer 3

No, it isn't possible. ECMAScript specification doesn't expose Enviroment Record objects to end user anywhere.

Answer 4

One way to see them is using console.dir to get all the scopes including closures scopes and their variables list. Example:

function factory(){
    var _secret = "Some secret";
    var i = 0;
    return function(){
        i++;    
        return _secret + i;
    }
}

var inside = factory();
inside(); // "Some secret1"
inside(); // "Some secret2"
console.dir(inside); // It shows you all variables in [[Scopes]] > Closure

Image of how you would see the console:

It works in Chromium based browsers.

Edit: Related answer with nested scopes in related question https://stackoverflow.com/a/66896639/2391782

Answer 5

Since the primary concept of a closure is scope, and vars inside a closure are private, there can be no way to achieve this without exposing them somehow, like via a method.

What are you really trying to achieve?