Question

我想在函数中访问文档中的数据，我处理Item，如何将变量document.date放在itemstring中？

function pagelist(items, res) {
    var db = db_login;
    result = "<html><body><ul>";
    items.forEach(function(item) {
        console.log(item)
        db.collection('insights').findById(item._id , function(error, document) {
            console.log(document)
            if (error || !document) {
                res.render('error', {});
            } else {
            **console.log(document.date) //this value is displayed**
            }
        })

        **console.log(document.date)//this value is undefind**

        itemstring = "<li>" + item._id + "<ul><li>" + item.textScore +
            "</li><li>" + item.created + "</li><li>" + item.document +
            "</li></ul></li>";
        result = result + itemstring;
    });
    result = result + "</ul></body></html>";
    return result;
}

Answer 1

当前答案都错过了一个关键点，你的“子”函数是来自asyn函数的回调。它在“父”函数的其余部分之前不会执行。

function pagelist(items, res) {
    // ... (1)
    items.forEach(function(item) {
        db.collection('insights').findById(item._id, function(error, document) {
            // this will not execute (4)
        });
        // before this (2)
    });
    // or this (3)
    // Actual order will be in that of (numbers)
    return result;
}

您唯一的选择是使父函数的行为与db函数的行为相同。即也让它asyn。

function pagelist(items, done) { // <= "done"
    items.forEach(function(item) {
        db.collection('insights').findById(item._id, function(error, document) {
            // Now you can call done with document that is available here
            done(document); // or done(document.date); w/e
        });
    // return result; // Returns are useless* in asyncs
}

无论你在哪里打电话给pagelist()传递回调函数“完成”并在那里做东西

app.use(function(req, res){
    pagelist(items, function(document){ // <= this will be the "done" function
        var itemstring = document.date;
        // do whatever you want with the document here.
        res.render(~);
        console.log(document.date);
    });
});

Answer 2

试试这个：将局部变量document分配给全局变量doc并在函数外部访问它;

function pagelist(items, res) {
     var db = db_login;
     var doc;
     result = "<html><body><ul>";
     items.forEach(function(item) {
        console.log(item)
        db.collection('insights').findById(item._id , function(error, document) {
        console.log(document)
        doc=document; // assignment of the local variable to global variable
        if (error || !document) {
            res.render('error', {});
            } else {
            console.log(document.date)
            }})

     console.log(doc.date) // here is use of global variable

     itemstring = "<li>" + item._id + "<ul><li>" + item.textScore +
       "</li><li>" + item.created + "</li><li>" + item.document +
       "</li></ul></li>";
      result = result + itemstring;
     });
    result = result + "</ul></body></html>";
    return result;
   }

享受：）

如何在父函数中访问变量？

2 个答案: