Question

我是Javascript的新手并回调函数。这是回电的正确方法吗？当我测试我得到一个无限循环。我想从数据库中检索并存储在一个对象的变量中，以便在getSport（）中使用。

constructor(matchid) {
    this.hasLoaded = false;
    this.matchid = mid;
    this.Match = {
        "sport": "baskt",
        "winner": -1,
    };
}
rload(callback) {
    this.hasLoaded = true;
    matchDataBaseRef.child(this.mid)
        .on("value", function (snapshot) {
            this.Match = snapshot.val();
            callback();
        });
}
get getSport() {
    if (!this.hasLoaded) {
        this.rload(this.getSport);
    }
    return this.Match['sport'];
}

Answer 1

That's not the right approach. You are trying to synchronize in this.getSport. Instead, you should have your initialization inside the callback and do not infinitely call it. Let's suppose you have something like this:

function myTask(params) {
    //do something
    params.callback();
    //do something
}

then you should not work with that like this unless you have a very good reason:

var foo = function() {
    myTask({callback: foo});
};

Instead of it, in most cases you need something like this:

var foo = function(cb) {
    myTask({callback: cb});
};

cb needs to be defined though separately. So do not pass the wrapper function as a callback if that is not precisely what you want to do.

与数据库的Javascript回调

1 个答案: