的确是javascript擅自完成了这件事情，给片文章读一下：

http://blog.carbonfive.com/2013/10/27/the-javascript-event-loop-explained/

@alaaf 多谢前辈，同时我搭配了以下网页的说明更了解 node 的处理方式，但想了解我这种情况不晓得要如何等待接收函数 _SearchUser 的回传结果呢？

http://www.ruanyifeng.com/blog/2013/10/event_loop.html

@alaaf 基本上我对setTimeout的是熟悉的，但目前的情况下，我还是第一次遇到。

补充了问题描述，请各位前辈多多拔刀相助。

一般解决方式为回调，还有可以用Promise之类的库。

@coolicer

前辈你好，经过一番折腾后处理为以下，您看看

还是有一些问题无法克服（无奈）

app.post('/create_member_check', function(req, res) {
	var Authenticate = function () {
		SearchUser(req.body.email, function (isExist) { 
			if (isExist === true)
				throw 101;
			else if (req.body.email === undefined || req.body.email == "")
				throw 102;
			else if (req.body.password === undefined || req.body.password == "")
				throw 103;
			else if (isExist === undefined)
				throw 104;

			var user = {
				"email": req.body.email,
				"password": req.body.password
			};
			AddUser(user);
			// 这个 return 无效
			return user;
		});
	}

	try {
		var userInfo = Authenticate();
	}
	catch (err) {
		var userInfo;
		if (err == 101)
			userInfo = "[Error] This account already exists.";
		else if (err == 102)
			userInfo = "[Error] Please key in 'email'.";
		else if (err == 103)
			userInfo = "[Error] Please key in 'password'.";
		else if (err == 104)
			userInfo = "[Fatal Error] SearchUser return 'undefined'.";
	}

	res.render("login_system/create_member_check", {
		layout: false,
		pagename: "create",
		authenticate: userInfo
	});
});

SearchUser = function (email, callback) {
	dbclient.query("SELECT * FROM user WHERE email = \"" + email + "\"", function (err, results) {
		if (err || results.length <= 0)
			callback(false);
		else
			callback(true);
	});
}

@grass0916

你的return无效，会不会是Adduser里面有其他的影响了

兄弟你别整的这么复杂，先从最简单的查询做起，把所有的步骤都放在回调里面，肯定能行。

试试把try catch， render 放在函数里给callback。

@coolicer @alaaf 感谢各位，我跌跌撞撞几次后终于有结果了

app.post('/create_member_check', function (req, res) {
	var Authenticate = function (req, callback) {
		SearchUser(req.body.email, function (isExist) { 
			if (isExist === true)
				return callback(101);
			else if (req.body.email === undefined || req.body.email == "")
				return callback(102);
			else if (req.body.password === undefined || req.body.password == "")
				return callback(103);
			else if (isExist === undefined)
				return callback(104);

			var user = {
				"email": req.body.email,
				"password": req.body.password
			};
			AddUser(user);
			callback(null, user);
		});
	}

	Authenticate(req, function (err, user) {
		var userInfo;
		if (err == 101)
			userInfo = "[Error] This account already exists.";
		else if (err == 102)
			userInfo = "[Error] Please key in 'email'.";
		else if (err == 103)
			userInfo = "[Error] Please key in 'password'.";
		else if (err == 104)
			userInfo = "[Fatal Error] SearchUser return 'undefined'.";
		else
			userInfo = "[Success] Created the account.";

		res.render("login_system/create_member_check", {
			layout: false,
			pagename: "create",
			authenticate: userInfo
		});
	});
});

@grass0916 看来callback用得很熟了。