if we want to transfer some variable to another page by ajax, we use data: {a: 1, b: 2} and it will send like xxx.php?a=1&b=2
but if a is not a constant variable, such as var $a = x data: {$a: 1} I want it become xxx.php?x=1 var $a = y data: {$a: 1} I want it become xxx.php?y=1 how to do that?