Checkbox checked and unchecked judgment example

$(document).ready(function() {
  var flag = $("#protTuanFlag").val();
  if(flag==1){
    document.getElementById("tuan").checked=true;
  };
  $("#tuan").click(function() {
    if(document.getElementById("tuan").checked){
      //Alert (" selected ");
       document.getElementById("tuan").value = 1;
       // alert(document.getElementById("tuan").value);
    }else{
      //Alert (" unchecked ");
       document.getElementById("tuan").value = 0;
       //alert(document.getElementById("tuan").value);
    }
  });
})