php - In jQuery.post, how do I get value of variable outside function?

Question

I have the following function:

var id = "10";
var type = "Type A";
var img = "myimage.jpg";

jQuery.post("my/path/somefile.php", { instance: 'getUrl', ID : id, type: type},
function(data)
{ 
    jQuery('#logo').attr("src",data.url + img);
},"json"); 

1. How can I get the value of img when I'm inside the function?
2. How can I sett img = new value from inside the function?

UPDATE

This code does NOT give a new value to the variable:

    logoUrl = "noLogo.png";

    jQuery.post("my/path/somefile.php", { instance: 'getUrl', ownerID : "123", type: "brand"},
    function(logo)
    {
        logoUrl = logo.url + "logo/";
    },"json");      

    alert(logoUrl); // This outputs noLogo.png"

Answer 1

UPDATE

When working with callback functions, its important to pay attention to execution flow:

var img = "nice.jpg";

$.post('/path', { key: value }, function(data){
   img = "newname.jpg";
});

alert(img); // Alerts "nice.jpg"

It is because any code occurring after the callback (but not in the callback function) is executed first:

1. Set img to nice.jpg
2. Call $.post
3. Call alert
4. Set img to newname.jpg

Original answer:

If the code you are using exists exactly as you posted it, then:

1. img is already available inside your anonymous callback function.
2. Yes, you can change the value of img from inside the function as well.

When you declare variable with the var keyword, it is private to its current scope, but is available to any other contexts contained within its scope:

WORKS

function getPost(){
   var img = "nice.jpg";

   $.post('/path', {key:value}, function(data){
       alert(img); // alerts "nice.jpg"
   });
}

DOES NOT WORK

function changeImage(){
   var img = "nice.jpg";
   getPost();
}

function getPost(){
   $.post('/path', {key:value}, function(data){
       alert(img); // img is undefined
   });
}