Question

function getPending(friendships) {
var myTable= "";
var userId = getUserId('username');
for(let key in friendships){
    if(friendships.hasOwnProperty(key)){
        if(friendships[key].recvId == userId) {
            // Do Something with it. Access it via users[key]
            myTable += "<div class='container'>";
            myTable += "<div class='row'>";
            myTable += "<div class = 'col-sm-4'>";
            var name ="";
            var ref = firebase.database().ref().child("Users");
            var foundUser = false;
            ref.orderByValue().on("value", function(snapshot) {
                snapshot.forEach(function(data) {
                    var user = data.val();
                    if(user.userId == friendships[key].sendId && foundUser == false) {
                        name += ("" + user.username);
                        foundUser = true;
                    }
                });
            });
            myTable += name + "</div>";
            myTable += "<div class = 'col-sm-4'>Be my friend!</div><div class = 'col-sm-4'>"
            myTable += "<button>Accept</button><button>Decline</button></div></div></div>"
            }
        }
    }
return myTable;
}

这是我的代码，用于显示所有待处理的好友请求。

return语句在for循环结束之前运行，并且每次实际返回一个空字符串。

我认为问题在于：ref.orderByValue().on("value", function(snapshot) { ....

如何在所有执行完成后强制javascript运行return语句？

Answer 1

这是正确的方法，首先你需要使用async库，所以先安装，然后就可以使用这样的代码了。

        function getPending(friendships, cb) {
            var myTable= "";
            var userId = getUserId('username');
            async.each(Object.keys(friendships), function(key, callback) {
                if(friendships[key].recvId == userId) {

                        ref.orderByValue().on("value", function(snapshot) {
                            snapshot.forEach(function(data) {
                                        // Do Something with it. Access it via users[key]
                                myTable += "<div class='container'>";
                                myTable += "<div class='row'>";
                                myTable += "<div class = 'col-sm-4'>";
                                var name ="";
                                var ref = firebase.database().ref().child("Users");
                                var foundUser = false;
                                var user = data.val();
                                if(user.userId == friendships[key].sendId && foundUser == false) {
                                    name += ("" + user.username);
                                    foundUser = true;
                                }
                                myTable += name + "</div>";
                                myTable += "<div class = 'col-sm-4'>Be my friend!</div><div class = 'col-sm-4'>"
                                myTable += "<button>Accept</button><button>Decline</button></div></div></div>"
                                callback();

                            });
                        });

                    }
            }, function(err) {
                cb(err, myTable)
            })
    }

你不能只是简单地返回表，它应该是回调，或者你可以修改返回承诺的方式

使用Firebase函数时如何等待在javascript中运行return语句

1 个答案: