.get请求始终成功状态

I have to get the content of page demo_test.php, but the status is always = success, while "data" print the code of the index main and then not of demo_test.php.

Also if I put an inexistent address.php, status is always = success.

 $.get("demo_test.php",function(data,status){
    alert("Data: " + status);
 });

Why ? Thanks.

$.get( "demo_test.php", function(data) {
  alert( "Data: "+data );
})
.fail(function() {
    alert( "We failed" );
 });