Simple Queue/Parallel exec in js

gistfile1.js

var q = function() {
    var args = _.flatten(arguments);
    var ctr = args.length;
    var complete;

    function run(i) {
      args[i](function() {
        if (i + 1 === ctr) {
          if (complete) {
            complete();
          }
        } else {
          run(i + 1);
        }
      });

    }

    run(0);

    return ({
      then: function(fn) {
        complete = fn;
      }
    });
  };

var parallel = function() {
    var args = _.flatten(arguments);
    var ctr = args.length;
    var complete;

    _.each(args, function(f) {
      f(function() {
        ctr--;
        if (ctr === 0) {
          if (complete) {
            complete();
          }
        }
      });
    });

    return ({
      then: function(fn) {
        complete = fn;
      }
    });
  };

q(function(done){
    setTimeout(function(){
        done();
    },3000);
}, function(done){
    setTimeout(function(){
        done();
    },5000);
} /* ,add more functions in the queue array */ ).then(function(){
    console.log('finished!')
});