how do I turn asynchronous to be false in my jquery ajax

how do I turn asynchronous to be false in my jquery ajax

Please how do I turn asynchronous to be false as async: false in my code bellow:
$.post("connect_ajax_php.php",
{type: "checkId", val: val, field: "emp_id", table: "employee"})
.done(function(data, succ){
data = $.trim(data);
if( succ =="success" && data=="true" ){
$( errContId ).html( val+" already exist" );
$( id ).css( {"border":"1px solid red"} );
return false;
}else{
$( errContId ).html("");
$( id ).css( {"border":"1px solid #ccc"} );
}
});