Javascript - How deeply can a variable retain its value?

Question

Noob question here. Please see code below. Where can I read more on this? I mean, this_variable gets 100. All subsequently defined functions seem to be able to access this variable and get it's value, but I wonder how deep does this work? I'm working on a Chrome extension and the damn thing only works with callbacks; I need to be able to access stuff within a pretty deeply nested callback and I need to be sure that what I write is reliable and will remain consistent.

(function(){

    this_variable = 100;

    (function(){
        (function(){
            (function(){
                (function(){
                    (function(){

                        tadaaa = this_variable;
                        console.log(tadaaa); // sais 100                

                    }());
                }());
            }());
        }());
    }());
}());

If it happens that `tadaaa` is somehow not set properly then it means that your computer is going to reboot in a second ;) — Tomasz Zieliński, Feb 16 '12 at 15:14

score 6 · Answer 1 · answered Feb 16 '12 at 15:11

6

There is no limit. Though if you're nested deeply enough to worry about a limit, I would question the overall design.

answered Feb 16 '12 at 15:11

James Montagne

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Though I wouldn't *necessarily* discourage deep nesting. That's how functional programming works after all. – George Mauer Feb 16 '12 at 15:15
Most of the chrome.* API is comprised of asynchronous functions. How else would I change the overall design? Working with the global scope? – Silviu-Marian Feb 16 '12 at 15:51
That's why I only said "question" the design. I can't see it so I don't know, it may be just fine. – James Montagne Feb 16 '12 at 15:53

score 2 · Answer 2 · answered Feb 16 '12 at 15:12

2

As long as a variable is 'in scope' it can be accessed (presuming it's not hidden). You can nest as much as you like. See here for scoping and closure reference from MDN.

answered Feb 16 '12 at 15:12

Rich O'Kelly

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score 2 · Accepted Answer · edited May 23 '17 at 09:59

2

As deeply as you want. The name for the concept is closures and it is the most important concept when programming advanced javascript.

edited May 23 '17 at 09:59

Community

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1

answered Feb 16 '12 at 15:12

George Mauer

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Yes, that's what they were called, closures. Thanks, I'll dig. – Silviu-Marian Feb 16 '12 at 21:03

score 1 · Answer 4 · answered Feb 16 '12 at 15:11

1

As far as you goes..

It might be slower at some point, but should still be accessible all the way through your callbacks.

answered Feb 16 '12 at 15:11

f2lollpll

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Greg Franko · Answer 5 · 2012-02-17T05:20:36.863

Javascript uses function scoping. The rule is if a variable is set within the top level function, then all of the nested functions within the top level function have access to that variable. If a variable is declared within a nested function, then the top level function(s) will not have access to that variable.

//Immediately invoked function that scopes jQuery and outside code cannot access
$(function() {
    //top-level function
    function test() {
        var a = true;
        //nested function
        function nestedTesting() {
            //The nested function has access to a
            console.log(a);
            var b = false;
        }
        nestedTesting();
        //The top level function does not have access to b
        console.log(b);
    }
    test();
});

Expected Result:

true
Uncaught ReferenceError: b is not defined

Javascript - How deeply can a variable retain its value?

5 Answers5