How Ajax passes multiple parameters

1.

var str=$ ("AP"). Find (' Resp_code '). html (); Gets the value that the rich friend returns inside the XML data
var contract_no=$ ("AP"). Find (' Contract_no '). html ();//Contract number
Assigns the value of the contract number to the hidden field
$ ("#contract_no"). Val (contract_no);
var user_name=$ ("#user_name"). Val ();
var mchnt_txn_ssn=$ ("#mchnt_txn_ssn"). Val ();
var height= $ (document). Height ();
var $L =document.documentelement.clientwidth;
var $H =document.documentelement.clientheight; Use JS to get the current client's high
var $CW =math.ceil ($ ('. Zzc-erro '). CSS (' width '). substr (0,3));
var $CH =math.ceil ($ ('. Zzc-erro '). CSS (' height '). substr (0,3));
if (str== "0000") {

$.ajax({
Type: "Post",
URL: ' 3.php?action=ok ',
Async:false,
data: {contract_no:contract_no, User_name:user_name, mchnt_txn_ssn:mchnt_txn_ssn},
Success:function (data) {


}
});

How Ajax passes multiple parameters