输入：选中在 IE9 中不起作用

Question

I made a simple modal that adds a series of records into some tables.
Before submitting the values I ask the user to check a radio to confirm the action.
When the radio is checked the submit button becomes clickable.
This works fine almost in every browser except for IE9 (and previous): in this browser I have to check the radio and then click on a blank point into the modal and only then the submit button becomes clickable.
This is a screenshot of the modal:

And this is the portion of the code interested:

 function checkAcconsento() {
    var acconsento = document.querySelector('input[name=acconsento]:checked').value;
    if (acconsento == 'S') {
        document.getElementById('btn_ins_corso').disabled = false;
        document.getElementById('btn_ins_corso').className = "btn_normale";
    } else {
        document.getElementById('btn_ins_corso').disabled = true;
        document.getElementById('btn_ins_corso').className = "";
    }
}

Answer 1

You an try the following, depending on different version of Jquery and browser

$('#element').is(':checked');
$('#element').attr('checked');

Answer 2

I have created a plunker here https://plnkr.co/edit/e3pcEO8mUIdomp4YxYrw?p=preview This works for me in IE 11.0.9 I have changed your method to this:

function checkAcconsento() {
    var acconsento = document.querySelector('input[name=acconsento]:checked');
    if (acconsento)
    {
      var val = acconsento.value;
      if (val == 'on') {
          document.getElementById('btn_ins_corso').disabled = false;
          document.getElementById('btn_ins_corso').className = "btn_normale";
      }   
    }
    else {
        document.getElementById('btn_ins_corso').disabled = true;
        document.getElementById('btn_ins_corso').className = "";
    }
}