请教Java里面的一段话的意思.看不懂

请教Java里面的一段话的意思.看不懂
function registerClick()
{
if(window.sessionStorage && window.localStorage)
{
var userName = document.getElementById('txtUserName');
var userPwd = document.getElementById('pwd');
window.sessionStorage[userName] = userName.value;
window.sessionStorage[userPwd] = userPwd.value;
window.localStorage[userName] = userName.value;
window.localStorage[userPwd] = userPwd.value;
window.open('refresh.html');
}
}