为什么我得到一个空的对象,当一个函数在node.js中被调用? [英] Why do I get an empty object when a function is invoked in node.js?
问题描述
我有这样的 app.get
在我的的node.js
防爆preSS服务器。
I have this app.get
in my node.js
Express Server.
app.get('/api/court/:num', function(req, res, next) {
var courts = new CourtsHandler;
if (req.params.num == 0) //get array of all courts
return res.send(200, courts.courtsAmount());
});
这是调用这个函数:
which is calling this function:
this.courtsAmount = function(){
connection.query('SELECT COUNT(*) AS result from courts', function(err, rows, fields){
if (err) throw err;
connection.end();
console.log(rows[0].result);
return rows[0].result;
});
};
该courtsAmount函数获取调用。但是,在我的客户视图,我没有得到的reuslt。相反,我只是得到一个空的对象。
The courtsAmount function is getting called. But in my client-view, I am not getting the reuslt. Instead I am just getting an empty object.
我认为这是与事实,我的 .query
有所回调,因而做 res.send
courtsAmount
实际上是发射之前将一个空的对象。
I assume this has to do with the fact that my .query
has a callback, and thus res.send
sends an empty object before courtsAmount
is actually fired.
我怎样才能解决这个问题?
How can I address this issue?
推荐答案
您courtsAmount不返回任何东西。相反,你应该使用它里面的回调(或承诺),做这样的事情:
Your courtsAmount doesn't return anything. Instead you should use a callback inside it (or a promise), to do something like this:
this.courtsAmount = function(callback){
connection.query('SELECT COUNT(*) AS result from courts', function(err, rows, fields){
if (err) throw err;
connection.end();
console.log(rows[0].result);
callback(rows[0].result);
});
};
和
app.get('/api/court/:num', function(req, res, next) {
var courts = new CourtsHandler;
if (req.params.num == 0) //get array of all courts
courts.courtsAmount(function(result) { res.send(200, result) });
});
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