Question

I need to make a condition based on data returned from an ajax post outside the post function

function post(){

   $.post('page.php',$('#form').serialize(), function(data) {
   if(data !== 'good'){alert(data); return false;} // take this out of here
});
    //and place it here

}

Answer 1

Code like below should work fine.

function post(){
   var data;
   $.ajax({url:'page.php',
           async:false,
           type:'POST',
           data:$('#form').serialize(), 
           success:function(res) {
                 data = res;
           }
     });
     if(data !== 'good'){alert(data); return false;} // take this out of here
}

But remember that synchronous ajax call will freeze your page until request is done and you may find it better to find a way how to do what you need without moving if(data !== 'good'){alert(data); return false;} outside success callback function.

UPD: missed to specify request type, which should be POST instead of default GET. Code updated.