Synchronous for loop in JavaScript to ensure that the n+1th item isn't processed until the callback of the nth item's processor has been called.

doSynchronousLoop.js

/**
 * Process an array of data synchronously.
 *
 * @param data An array of data.
 * @param processData A function that processes an item of data.
 *                    Signature: function(item, i, callback), where {@code item} is the i'th item,
 *                               {@code i} is the loop index value and {@code calback} is the
 *                               parameterless function to call on completion of processing an item.
 */
function doSynchronousLoop(data, processData, done) {
	if (data.length > 0) {
		var loop = function(data, i, processData, done) {
			processData(data[i], i, function() {
				if (++i < data.length) {
					loop(data, i, processData, done);
				} else {
					done();
				}
			});
		};
		loop(data, 0, processData, done);
	} else {
		done();
	}
}

And what about https://github.com/caolan/async ?

This was just a learning exercise for me and I posted it here for myself, but I made it public because there's no reason to hide it.

i love this <3

Very useful for me..! :-*

You'll run easily into the maximum off call stacks. Workaround:

function doSynchronousLoop(data, processData, done) {
    if (data.length > 0) {
        var loop = function(data, i, processData, done) {
            processData(data[i], i, function() {
                if (++i < data.length) {
                    setTimeout(function(){
                                            loop(data, i, processData, done);
                                        }, 0);
                } else {
                    done();
                }
            });
        };
        loop(data, 0, processData, done);
    } else {
        done();
    }
}

Genius! worked like a charm. Can we have a little bit of an explanation about why this works? :)

Nice work !!! Kind of a cool way to implement sync loops 👍

Pure genius!

Nice work!!!!!!!!!!!!! you are genius!

Nice!