Using Javascript sessionStorage versus Cookies


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Using Javascript sessionStorage versus Cookies

In browsers that support HTML5 we can use sessionStorage in Javascript instead of Cookies to set variables that need to be persistent per session.

For example, in this PHP code for the forums, we can do something like the following:

Code:
$localStorage  = '<script>'; 
$sessionStorage .= 'sessionStorage.setItem("showMember","true");'; 
$sessionStorage .= 'sessionStorage.setItem("thisScript","'.THIS_SCRIPT.'");'; 
$sessionStorage .= 'sessionStorage.setItem("styleId","'.STYLEID.'");'; 
$sessionStorage .= 'sessionStorage.setItem("userId","'.USER_ID.'");'; 
$sessionStorage .= '</script>'."\n";

And of course insert the code above in our HTML template somewhere (like the header) and then use the sessionStorage vars (from our server side PHP code) in our Javascript and jQuery scripts.

The main difference is that the data stored in sessionStorage is not sent back to the server per request (like in Cookies) and the storage limit is much bigger for sessionStorage than for Cookies.

In HTML5 sessionStorage differs primarily from localStorage in that localStorage does not go away even after the tab or browser is closed. It can of course be cleared with the localStorage.clear() method or cleared in browser by the user.

Here is a small example of how we use sessionStorage:

Code:
<script>
$(function() {
  if(sessionStorage.showMember && sessionStorage.thisScript !='showpost')
  {
    var text =  document.getElementById("neo-notice").innerHTML;
    var unread = text.match(/>0<\/strong>/g);
     if(!unread){
       $('.avatarbadge').show();
     }
      else {  $('.avatarbadge').hide();}
  }
});
</script>

In the code above, we are trapping an error because of some strange bug on one of our pages when we show notifications to users. Otherwise, we check for messages unread and if so, we display the badge.

Here is another example:

Code:
<script>
$(document).ready(function() {
if(sessionStorage.showMember && sessionStorage.thisScript != 'showpost')
 {
  if ($('#myMemberPanel').length > 0) {
  document.getElementById("myMemberPanel").style.width = "0px";
 }
}
});
</script>

In the above example, we trap the same error (on the 'showpost' pages which we have deprecated) and otherwise we set the initial width of the memberPanel to 0px;

These are fairly trivial examples, but they do help illustrate how easy it it is in HTML5 to use localStorage and sessionStorage in Javascript.

Last edited by Don Cragun; 10-14-2018 at 01:58 PM.. Reason: Move "<script>" inside CODE tags.
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