Based on the original sync gist -- https://gist.github.com/catdad/4598289 -- this code will execute asynchronous functions synchronously, passing the result of one function as the seed data of the next.

waterfall.js

//simple sync function
function sync(/* funcsArray, done, seedDataArgs */) {
    var args = Array.prototype.slice.call(arguments, 0);
    //functions array to sync is first
	var funcs = args.shift();
	//done callback is second
    var done = args.shift();
	//all remaining arguments are the seed data
    
    var counter = funcs.length;
    var idx = 0;

    var next = function () {
        //console.log("inside next");
        var privateArgs = Array.prototype.slice.call(arguments, 0);
        privateArgs.push(next);
        if (--counter === 0) done && done.apply(null, privateArgs);
        else funcs[idx++].apply(null, privateArgs);
    };
    
	//add the next callback as the last argument
    args.push(next)
    funcs[idx++].apply(null, args);
}