pass parameter from $.post() callback to outer variable

Question

basically i want to hold a parameter that retrieve value from $.post() call like this:

init = function(){          
var lastpage = getLastPage();
}

        function getLastPage(){
            $.post("getInfo.php",{ 
                last: "yes"
            },
            function(data){
                setLast(data.last);
            },'json');

            return function setLast(data){
                return data;
            }
        }

so when reach at last post (last page) i should check with lastpage variable that has a value returned from getLastPage() function.

I'm pretty blur with javascript pointer and all. Please help guys.

update (20/4/2010):

I've done the other way around, like this:

init = function(){            
  getLastPage();
  if((page+1) == $("#lastpage").val()){
     alert("this is last post");
  }else{
     page++;
     //get info and display to the page here
  }
}
     function getLastPage(){
        $.post("getInfo.php",{ 
            last: "yes"
        },
        function(data){
            $("#lastpage").val(data.last);
        },'json');
    }

first run the function to temporarily store the value in hidden input tag (lastpage) and then grab the value again to check it whenever i click forward button.

if you all have more appropriate way please tell me.

Answer 1

You should change your code around like this:

$.post("getInfo.php",{ last: "yes" },
  function(data){ 
    functionToRunAfterYouHaveDataSometimeLater(data.last); 
  }
,'json');

The problem with your overall approach is that with AJAX, you're dealing with an asynchronous operation. This means that the function(data) { } portion doesn't run then, it runs later, so your return doesn't actually return anything, it'll be undefined.

Instead of this approach, you need to call $.post() then call whatever function relies on this data to continue as part of $.post()'s callback. After doing that your code order looks like this:

• $.post() executes, firing off a request to the server
• The rest of your code after $.post() runs
• Later when the response comes from the server and you have data, your callback executes
• Now continue to do what you need with that data