Why does foo = "" while obj = {foo: "bar"}?

gistfile1.js

var getFoo = function(){
    var val = "";
    $.get(".", function(){
        val = {foo: "bar"};
    });
    return val;
}

var foo = getFoo();
// foo = ""

var getObj = function(){
    var obj = {};
    $.get(".", function(){
        obj.foo = "bar";
    });
    return obj;
}

var obj = getObj();
// obj = {foo: "bar"}