从函数返回结果（javascript，nodejs）
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return results from a function (javascript, nodejs)
提问by profesoralex
Could anyone help me with this code? I need to return a value form a routeToRoom function:
任何人都可以帮助我使用此代码吗？我需要从 routeToRoom 函数返回一个值：
var sys = require('sys');
function routeToRoom(userId, passw) {
var roomId = 0;
var nStore = require('nstore/lib/nstore').extend(require('nstore/lib/nstore/query')());
var users = nStore.new('data/users.db', function() {
users.find({
user: userId,
pass: passw
}, (function(err, results) {
if (err) {
roomId = -1;
} else {
roomId = results.creationix.room;
}
}
));
});
return roomId;
}
sys.puts(routeToRoom("alex", "123"));
But I get always: 0
但我总是得到：0
I guess return roomId;is executed before roomId=results.creationix.room. Could someone help me with this code?
我猜return roomId;是之前执行的roomId=results.creationix.room。有人可以帮助我使用此代码吗？
回答by Raynos
function routeToRoom(userId, passw, cb) {
var roomId = 0;
var nStore = require('nstore/lib/nstore').extend(require('nstore/lib/nstore/query')());
var users = nStore.new('data/users.db', function() {
users.find({
user: userId,
pass: passw
}, function(err, results) {
if (err) {
roomId = -1;
} else {
roomId = results.creationix.room;
}
cb(roomId);
});
});
}
routeToRoom("alex", "123", function(id) {
console.log(id);
});
You need to use callbacks. That's how asynchronous IO works. Btw sys.putsis deprecated
您需要使用回调。这就是异步 IO 的工作原理。顺便说一句sys.puts已弃用
回答by Simone Gianni
You are trying to execute an asynchronous functionin a synchronous way, which is unfortunately not possible in Javascript.
您正在尝试以an asynchronous function同步方式执行，不幸的是not possible in Javascript。
As you guessed correctly, the roomId=results.... is executed when the loading from the DB completes, which is done asynchronously, so AFTER the resto of your code is completed.
正如您猜对的那样，roomId=results.... 在从数据库加载完成时执行，这是异步完成的，因此在您的代码恢复完成后。
Look at this article, it talks about .insert and not .find, but the idea is the same : http://metaduck.com/01-asynchronous-iteration-patterns.html
看这篇文章，讲的是.insert and not .find，但是思路是一样的：http: //metaduck.com/01-asynchronous-iteration-patterns.html
