Useful example of base variables referenced in a callback remaining in scope

js_callback_scope_ex.js

// adapted from displayAppFiles() in app.js

function checkIfAnyFiles() {
    var items_found = 0; // variable defined in outer function
    
    var each_item = function(result) {
        items_found++; // still in scope for the callback
    }
    var when_done = function () {
        // Output depends on number of items traversed by each_item
        console.log('found ' + items_found + ' files'); 
        if (items_found == 0) { 
            // ... write 'no files found' to the listview
        }
    }
    
    enumerateFiles({ // ... ,
        func_each: each_item, // functions are only called inside #enumerateFiles
        func_done: when_done
    });
}