variable no accessible after a Firebase call [duplicate]

问题

This question already has answers here:

Passing variable in parent scope to callback function (3 answers)

Closed 4 years ago.

I'm using Firebase to access to same data, but i can't use the data out of the function used to access it. How i can make a console log of the data just accessed instead of the initial value?

var whatNeed = 'hello';
gameData = new Firebase('https://thegame.firebaseio.com/gameData');
    gameData.on("value", function(snapshot) {
        var data = snapshot.val();
        whatNeed = data.property;
    });
console.log(whatNeed);

回答1:

whatNeed will always contain the initial value when called outside of your callback as the console.log will be called first since the value event handler is asynchronous.

来源：https://stackoverflow.com/questions/27474546/variable-no-accessible-after-a-firebase-call