jQuery checkbox check all, but if one not checked, primary checkbox become uncheck

check-recheck.js

// document ready
$(document).ready(function() {
  
  // event on change
  $(document).on("change","#box-all",function() {
      // check all
      if(this.checked) {
          $(".box-single").each(function() {
              this.checked = true;
          })
      // un-check all
      } else {
          $(".box-single").each(function() {
              this.checked = false;
          })              
      }
  });

  // event on click
  $(document).on("click",".box-single",function() {
    // if all check box single are checked
    if ($(this).is(":checked")) {
      var isAllChecked = 0;
      $(".box-single").each(function() {
        if(!this.checked) isAllChecked = 1;
      })
      // box all get check
      if(isAllChecked == 0) $("#box-all").prop("checked", true);
    } else {
      // box all get un-check
      $("#box-all").prop("checked", false);
    }
  });
  
});