无法从javascript / nodejs中的全局变量中检索数据[重复]

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How do I return the response from an asynchronous call? 30 answers
如何从异步调用返回响应？ 30个答案

I'm trying to put data into an object. Although this object in loop has value, this object out of the loop hasn't value (empty). I had instance object global variable obj. What's wrong with me?

我正在尝试将数据放入对象中。尽管循环中的此对象具有值，但此循环外的对象没有值（空）。我有实例对象全局变量obj。我怎么了？

p.s : findOne is a mongoose's method. (mongodb).

p.s：findOne是一种猫鼬的方法。（MongoDB的）。

var obj = [];
for(var i = 0;i<anotherObj.length;i++){
    var id = anotherObj[i].id;
    model.findOne({_id:id},function(err,user){
        if(!err){
            obj.push(user);
            console.log(obj); /* <= it has value */
        }
    })
}

      console.log(obj);  /* <= this is null */

2 个解决方案

#1

Your findOne callback runs asynchronous, meaning that your last console.log runs before you push the user to the obj (array).

您的findOne回调运行异步，这意味着在将用户推送到obj（数组）之前，您的上一个console.log运行。

You would need to call a function after every user in the loop has been fetched. Try the async package

在获取循环中的每个用户之后，您需要调用一个函数。尝试使用异步包

#2

Your query to mongoose are asynchronous. The callbacks will be executed only on the next iteration of the event loop/when the data is available. That is why you see the obj being null.

您对mongoose的查询是异步的。回调将仅在事件循环的下一次迭代/数据可用时执行。这就是为什么你看到obj为null的原因。

#1