nodejs的异步蛋疼死了..：报错

function step_final()
{
	return function(content) {
		if (content == "fsda") {
			alert("END")
		} else {
			alert("asdf")
		}
	}
}

function step1(nextstep)
{
        var count = 1
        return function(content) {
		count = count + 1
                if (count % 5 == 0) {
                       nextstep("fsda")
                } else {
                       nextstep(content)
                }
	}
}

function httphandl(nextstep)
{
	var content = ""
	return function(req, res){
		if (res == "END") {
			nextstep(content)
			content = ""
		} else {
			content = content + res
		}
	}
}

var handl = httphandl(step1(step_final()))

http.createserver(handl)