Question

If i have a function like this

function do(callback) {
  //do stuff
  callback();
}

and then I pass in an anonymous function:

do(function() { //do something else });

does that anonymous function ever get collected during the lifespan of the page? If not, how can i make it available for GC?

do I have to do this?

var h = function() { //do something };
do(h);
delete h;

Do I even have to worry about this? I am building a web app that has a long lifespan, makes a lot of ajax calls keeps objects for a while and doesn’t really require a page refresh to navigate thru. So I’m trying to figure out if I might fall into a memory leak monster.

Answer 1

The only reference to the anonymous function is the function argument, and that disappears when the function finishes, so your callback will be available for garbage collection after that. Except when something else gets a reference to it, which can happen easily with closures:

function doo(callback) {
    $.get(url, function() {
        // callback is visible here!
    });
    callback();
}
doo(function() { /* do something else */ });

callback (along with the whole scope created by calling doo) must stay in the memory, because the inner function can reference it through the closure; it can only be garbage collected when the inner function is garbage collected, and since that function is a property of the jqXHR object, that object must be garbage collected before that, and who knows when that will happen…

Update You can avoid unnecessary closures by not defining your functions inside other functions:

var func = function() {
    // callback is not visible here
}
function doo(callback) {
    $.get(url, func);
    callback();
}
doo(function() { /* do something else */ });