jqeury ajax not returning false

jqeury ajax not returning false

I am new here. My program bellow checks if employee id exists using jquery ajax. I want it to return false if the employee id already exists but its not returning false.
$.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"} );
}
});