JQGrid add nvaigation button dynamically

I am using JQgrid and trying to navButtonAdd dynamically. from php side I am passing array with all require information like
$jqGrid->navButtonAdd=array(
array("caption"=>"Add Button1","buttonicon"=>"ui-icon-plusthick","onClickButton"=>"button1_function","cursor"=>"pointer","position"=>"last"),
array("caption"=>"Add Button2","buttonicon"=>"ui-icon-plusthick","onClickButton"=>"button2_function","cursor"=>"pointer","position"=>"last")
at my javascript page I am getting this array values and make button in this way:
var navButtonAdd = data.navButtonAdd;
var captionName;
var functionName=;
var buttonIcon;
if(typeof(navButtonAdd) !='undefined'){
for (t=0; t< navButtonAdd.length; t++ ){
if(navButtonAdd[t].caption !='undefined'){
captionName=navButtonAdd[t].caption;
}
if(navButtonAdd[t].buttonicon !='undefined'){
buttonIcon=navButtonAdd[t].buttonicon;
}
if(navButtonAdd[t].onClickButton !='undefined'){
functionName=navButtonAdd[t].onClickButton;
}
console.log(functionName);
//
$("#gridreport").jqGrid('navButtonAdd',"#pgridreport",{
caption:captionName,
buttonicon:buttonIcon,
onClickButton:function () {
var arguments;
//eval(callFunction)(param);
alert(functionName);
if(functionName)
windowfunctionName;
},
position:navButtonAdd[t].position

                });

           }
          } 
        );

Problem: my code make all button correctly but not bind correct function with each button when I click on button it always call "button2_function" can anybody help to me how to I call correct function on click of every button thanks in advance....