Get Checkbox total count & save value in textbox if checked

I have written below code to get a total count of Checked chechbox and save the value checked value comma separated in textbox.

HTML:

<label class='checkbox-inline'><input type='checkbox' class='checkbox-btn' value='1' onchange='checkCount(this.value);'></label>
<label class='checkbox-inline'><input type='checkbox' class='checkbox-btn' value='2' onchange='checkCount(this.value);'></label>
<label class='checkbox-inline'><input type='checkbox' class='checkbox-btn' value='3' onchange='checkCount(this.value);'></label>

<input type="text" name="proId" id="proId">

JS:

function checkCount(elm) {
  var cheCount = $(":checkbox:checked").length;
  document.getElementById('selectCount').innerHTML = cheCount;

  definVal = document.getElementById('proId').value ;
  var inval = elm+","+definVal;
  document.getElementById('proId').value = inval;

  if(cheCount==0){
    document.getElementById('proId').value = "";
  }
}

Check the output in below image:

My issue is that, when i unchecked the checkbox, its value is adding in textbox instead of getting remove.