var gridId     = "productsList"; //set to the ID of the grid
var checkboxId = "shipAbroad";   //set to the ID of the checkbox field inside the grid
var checkboxColNo = 0;           //set to the column number of the checkbox (start counting from zero); 

var reGridField = new RegExp("^\\["+gridId+"\\]\\[(\\d+)\\]\\["+checkboxId+"\\]$");
var formId = $("form").prop("id");

$("#"+formId).setOnchange( function(fieldId, newVal, oldVal) {
  var aMatch = fieldId.match(reGridField);
  
  //if the checkbox was marked in the grid, then unmark the checkbox in all other rows in the grid:
  if (aMatch && newVal == '"1"') {
    var selectedRowNo = aMatch[1] - 1; //subtract 1 because start counting grid rows from zero
    var aGridVals = $("#"+gridId).getValue();
    
    //loop through the grid looked for other marked rows:
    for (var i = 0; i < aGridVals.length; i++) {
      
      //if the checkbox in the row is marked and not the currently selected row, then unmark it:
      if (aGridVals[i][checkboxColNo] == '1' && i != selectedRowNo) { 
        //add 1 to row and column numbers because setValue() starts counting from 1, not 0:
        var aGridVals = $("#"+gridId).setValue('0', i+1, checkboxColNo+1);
      }
    }  
  }   
})


//when the form is submitted, make sure that one checkbox in the grid is marked:
$("#"+formId).setOnSubmit( function() {
  var aGridVals = $("#"+gridId).getValue();
  var markedRowNo = null;
    
  //loop through the grid to check that there is one marked checkbox in the grid:
  for (var i = 0; i < aGridVals.length; i++) {
    if (aGridVals[i][checkboxColNo] == '1') {
      if (markedRowNo) {
        alert("Both rows "+markedRowNo+" and "+(i+1)+" cannot be marked. Please only select one.");
        return false; //stop the submit action
      }
      
      markedRowNo = i+1;
    }
   
    if (markedRowNo === null) {
      alert("One row in the grid must be marked in the row.");
      return false;
    }
  }  
})