//initial checkCount of zero
var checkCount=0

//maximum number of allowed checked boxes
var maxChecks=2

function setChecks(obj)
{
    //increment/decrement checkCount
    if(obj.checked)
    {
        checkCount=checkCount+1
    }
    else
    {
    checkCount=checkCount-1
    }

    //if they checked a maxChecks+1 box, uncheck the box, then decrement checkcount and pop alert
    if (checkCount>maxChecks)
    {
        obj.checked=false
        checkCount=checkCount-1
        alert('Please only select a maximum of '+maxChecks+' checkboxes')
    }
}