ctl = ctl.replace( /<br />&nbsp;$/, '' );

it could be fixed by :

ctl = ctl.replace( /<br \\/>&nbsp;$/, '' );

let's say I have 3 checkboxes:

test1 checked

test  not_checked

test3 checked

the value are saved in the database. Next time I want to edit the records the "test1" and "text3" should be already checked when openening the form. I tried to modifiy your script but couldn't find out how to bring the values from the json dataset to your function...

Within the colModel, the appropriate edit fields look like this:

edittype:'custom'

editoptions:{ custom_element:MultiCheckElem, custom_value:MultiCheckVal, list:'Check1,Check2,Check3,Check4' }

Here are the javascript functions (BTW, It also works - with some modifications - when the list of checkboxes is in a DIV block):

//------------------------------------------------------------
// Description:
//   MultiCheckElem is the "custom_element" function that builds the custom multiple check box input
//   element. From what I have gathered, jqGrid calls this the first time the form is launched. After
//   that, only the "custom_value" function is called.
//
//   The full list of checkboxes is in the jqGrid "editoptions" section "list" tag (in the options
//   parameter).
//------------------------------------------------------------
function MultiCheckElem( value, options )
{
   //----------
   // for each checkbox in the list
   //   build the input element
   //   set the initial "checked" status
   // endfor
   //----------
   var ctl = '';
   var ckboxAry = options.list.split(',');

   for ( var i in ckboxAry )
   {
      var item = ckboxAry[i];
      ctl += '<input type="checkbox" ';

      if ( value.indexOf(item + '|') != -1 )
         ctl += 'checked="checked" ';
      ctl += 'value="' + item + '"> ' + item + '</input><br />&nbsp;';
   }

   ctl = ctl.replace( /\<br \/\>\&nbsp;$/, '' );
   return ctl;
}

//------------------------------------------------------------
// Description:
//   MultiCheckVal is the "custom_value" function for the custom multiple check box input element. It
//   appears that jqGrid invokes this function the first time the form is submitted and, the rest of
//   the time, when the form is launched (action = set) and when it is submitted (action = 'get').
//------------------------------------------------------------
function MultiCheckVal(elem, action, val)
{
   var items = '';
   if (action == 'get') // the form has been submitted
   {
      //----------
      // for each input element
      //   if it's checked, add it to the list of items
      // endfor
      //----------
      for (var i in elem)
      {
         if (elem[i].tagName == 'INPUT' && elem[i].checked )
            items += elem[i].value + ',';
      }

      // items contains a comma delimited list that is returned as the result of the element
      items = items.replace(/\,$/, '');
   }
   else // the form is launched
   {
      //----------
      // for each input element
      //   based on the input value, set the checked status
      // endfor
      //----------
      for (var i in elem)
      {
         if (elem[i].tagName == 'INPUT')
         {
            if (val.indexOf(elem[i].value + '|') == -1)
               elem[i].checked = false;
            else
               elem[i].checked = true;
         }
      } // endfor
   }

   return items;
}