从javascript对象方法回调中检索变量

Question

In my code I need to call an object method, retrieve the data from its callback, and pass it to another method or function.

someObject.getSomeData({option1:'value1', option2:'value2'},
    function(data) {
        doAwesomeStuff(data);
    }
);

However, the callback does not recognize any functions/objects/variables outside its scope.

What I've tried to do right now is wrap everything around a function.

var myData = '';
(function(myData) {
    someObject.getSomeData({option1:'value1', option2:'value2'},
        function(data) {
            myData = data;
        }
    );
});
doAwesomeStuff(myData);

However that doesn't work either.

Anybody know how to properly accomplish this?

Answer 1

You haven't really given us enough to go on there, but this statement:

However, the callback does not recognize any functions/objects/variables outside its scope.

...is incorrect. A function has access to everything in scope where it's defined, so for instance:

var a = 10;
function foo(b) {
    bar(5);
    function bar(c) {
        alert(a + b + c);
    }
}
foo(12); // alerts "27"

Note how bar had access not only to c , but also to b (from the call to foo ) and a (from the outermost scope shown).

So in your example, the anonymous function you're passing in as the callback has access to everything that's in scope where it's defined; doAwesomeStuff having been defined elsewhere presumably has access to different information, so you'll have to have the callback pass it any data it needs.

So I'm guessing your code looks something like this:

function doAwesomeStuff(data) {
    // ...
}

function doSomethingNifty() {
    var a = 10,
        b = 20;
    someObject.getSomeData({option1:'value1', option2:'value2'},
        function(data) {
            doAwesomeStuff(data);
        }
    );
}

...and you want doAwesomeStuff to have access to a and b from the call to doSomethingNifty . If so, your only options are to pass them into it as arguments (probably best) or export them to variables some scope that doSomethingNifty and doAwesomeStuff share (probably not ideal, too much like globals).

Answer 2

You can bind required variables to the function passed into the async method.

Also, this SO question has a good treatment of the topic.

Your second version is not going to work at all, since you are trying to immediately access the data that are not yet available (not until the callback has been invoked.)

Answer 3

Your first method:

someObject.getSomeData({option1:'value1', option2:'value2'},
    function(data) {
        doAwesomeStuff(data);
    }
);

looks fine. Please provide more details on what is not working.

One problem could be that getSomeData() does not actually call the callback function.

doAwesomeStuff() can modify many different variables from the received data. The variables which can be accessed by doAwesomeStuff() are those that were available to it (in its scope ) where it was created..