How do I execute a function after the callbacks inside a for loop are completed?

Question

I have a for loop in a search function, with a function that does a callback that does a callback inside the loop, and I want to execute a BUILD() function after the loop, and a

Answer 1

With a small modification of your code, it can be achieved.

var total = 1337; // Some number
var internal_counter = 0;
var fn_callback = function() {
    searchCallback.apply(this, arguments);
    if (++internal_counter === total) {
        BUILD();
    }
};
for (var i=0; i

Explanation

First, we create a local function and variable.

• The variable is a counter, which is increased when the callback is called.
• The function is passed to the asynchronous method (service.search), which calls the original callback. After increasing the counter, check the value of the counter against the variable which holds the total number of iterations. If these are equal, call the finishing function (BUILD).

A complex case: Dealing with nested callbacks.

var types = { '...' : ' ... ' };

function search() {
    var keys = Object.keys(types);
    var total = keys.length;
    // This counter keeps track of the number of completely finished callbacks
    //  (search_callback has run AND all of its details_callbacks has run)
    var internal_counter = 0;

    for (var i=0; i

The function logic is explained in the comments. I prefixed the heading of this section with "Complex", because the function makes use of nested local functions and variables. A visual explanation:

var types, BUILD;
function search
    var keys, total, internal_counter, fn_searchCallback;
    function fn_searchCallback
        var result, status; // Declared in the formal arguments
        var local_counter, i, fn_detailsCallback;
        function fn_detailsCallback
            var result, status; // Declared in the formal arguments

In the previous picture, each indention level means a new scope Explanaation on MDN.
When a function is called, say, 42 times, then 42 new local scopes are created, which share the same parent scope. Within a scope, declared variables are not visible to the parent scope. Though variables in the parent scope can be read and updated by variables in the "child" scope, provided that you don't declare a variable with the same name. This feature is used in my answer's function.