var x = {
    doSmth: function(param){
        var ret;
        $.getJSON(
            'ajax/someAct',
            {id: param},
            function(data) {
                if (data.result == 'success') {
                    ret = data.html
                };
            }
        )
        return ret;
    },
    doAnother: function(){
        var r = this.doSmth(123);
        alert(r);
    }
};
x.doAnother();