function doFirst(){
    var button = document.getElementById('button');
    button.addEventListener("click",save,false);
}

function save(){
    var FirstName = document.getElementById('FName').value;
    var LastName = document.getElementById('LName').value;
    localStorage.setItem(FirstName, LastName);
}


if(sessionStorage && window.onload === true){
    sessionStorage.clear('Fname', 'LName');
}

window.addEventListener("load",doFirst,false);