如何在facebook init函数javascript中设置标志？

Question

I have a sample code:

function initFB() {
    var flag;
    window.fbAsyncInit = function() {
        FB.init({appId: 'zzzzzz', status: true, cookie: true, xfbml: true});

        var flag;
        FB.getLoginStatus(function(response) {
            if (response.status === 'connected') {
                flag = 1;
            } else if (response.status === 'not_authorized') {
                flag = 2;
            } else {
                flag = 3;
            }
        });    
    };
    return flag;
}

var flag = initFB();
alert(flag); 

=> result is undefined , Can't set flag in facebook function ?, If not, how to fix it ?

Answer 1

What I would suggest you to do is to use a callback (probably anonymous), as the functions fbAsyncInit and getLoginStatus functions are both asynchronous (which means that they won't return something right away - they have to call facebook first, and after they've done so, they call their own callback (the function() { part)).

function initFB(callback) {
    window.fbAsyncInit = function() {
        FB.init({appId: 'zzzzzz', status: true, cookie: true, xfbml: true});

        FB.getLoginStatus(function(response) {
            var flag;
            if (response.status === 'connected') {
                flag = 1;
            } else if (response.status === 'not_authorized') {
                flag = 2;
            } else {
                flag = 3;
            }
            callback(flag);
            /* This will call the anonymous function specified as 
               "callback" with a parameter of whatever is in the 
               "flag" variable. */
        });    
    };
}

/* Here we use an anonymous function as a callback of 
   when getLoginStatus has gotten it's return value */
initFB(function(flag) {
    alert(flag); 
});

Answer 2

That is a scope and sync problem. The second time you define "flag" it´s only visible inside of the fbAsyncInit function, no connection to the "flag" variable on the outside. Also, the code in the fbAsyncInit function will get called later, when "flag" on the outside already got returned.