set cookie

function setCookie(name, value, expiredays ) {

  var todayDate = new Date();

  todayDate.setDate( todayDate.getDate() + expiredays );

  document.cookiｅ = name + "=" + escape( value ) + "; path=/; expires=" + todayDate.toGMTString() + ";"

}

function hideMe(){

if(document.popForm.chkbox1.checked == true ) {

setCookie("mainPop1", "done" , 1 );

document.getElementById('chkbox1').checked = false;

}

document.getElementById('divpop1').style.display="none";

}

<script type="text/javascript">

cookiedata = document.cookiｅ;

if(cookiedata.indexOf("mainPop1=done") < 0 ) {

document.getElementById('divpop1').style.visibility = "visible";

}

else{

document.getElementById('divpop1').style.visibility = "hidden";

}

</script>