callback lock queue - simple way to make functions that rely on callbacks execute serially.

lock.js

/*
 * return an object with two functions
 * push - push an invocation of t.f(args) which will be called immediately if the q is empty
 * next - the function that should be called in f to signal that the next invocation can be run
 * important! - every function given to push should call next
 */
function lock() {
	var q = [], busy = false;
	return {
		push: function(f, args, t) {
			if(!busy) {
				busy = true;
				f.apply(t, args);
			}
			else {
				q.push({f: f, args: args, t: t});
			}
		},
		next: function() {
			if(q.length > 0) {
				var n = q.shift();
				n.f.apply(n.t, n.args);
			}
			else {
				busy = false;
			}
		}
	};
}