jQuery全局变量$ .post（）;

$.post("general.php", {/* some values */}, function(data){var id = data;});
alert(id);

The problem is that, alert is empty. Do know anyone why? And how to fix it? Thanks.

There are 2 problems :

• one is that the ajax is asynchronous and the alert executes before the ajax callback, where the id variable is being set

• the second one is that the variable is not global, it is only visible in the callback scope

So, I suggest you declare the variable global (if you need it for later use) :

var id;// in the global scope

or

window.id = '';

And you should probably execute the logic in the callback :

$.post("general.php", {/* some values */}, function(data){ 
    window.id = data;
    alert(data);
});