Skip to main content

An odd behavior with localStorage events in HTML5

Today I was looking into web storage (localStorage) feature introduced in HTML5. Most of the modern browsers provide means through which key/value pairs can be securely stored and retrieved for later use. Browser cookies can indeed be used for the storage of persistent data but are limited in capacity. Also with cookies, the data is transmitted in every HTTP request thereby making the web applications run slow. Unlike cookies, in local storage there is no limit on the size of the data and it is never transmitted to the web server unless an attempt is made to send it manually. Whenever the data in the storage area changes a 'storage' event is fired. This event is fired whenever the methods setItem(), removeItem(), or clear() are called on the localStorage object.


However, when I tried to use these methods to update the localStorage area, the storage event never fired:

The methods setItem and clear did change the storage area and I confirmed this by referring to the resources  section in chrome developer tools. This looked very odd, but on referring to the w3c specification I found this: "When the setItem(), removeItem(), and clear() methods are called on a Storage object x that is associated with a local storage area, if the methods did something, then in every Document object whose Window object's localStorage attribute's Storage object is associated with the same storage area, other than x, a storage event must be fired". This meant that, the storage event would be fired in any other window\tab which used the same storage area.

Now on opening another tab and on clicking the Add\Clear button the localStorage area was affected and a storage event was fired in the other tab; not on the one that invoked the setItem or clear method. In a way this makes sense because the invoking window would already know of event and would perform the necessary action. Windows that share the same storage area would then be notified of the event and can update the DOM or perform the required action.


Labels:

Comments

  1. Janice ClementsDecember 8, 2011 at 3:00 PM

    That's a very odd behavior and I didn't know that until you posted this blog. Now I can probably deal it.

    Laptop Repair Services

    ReplyDelete

Post a Comment

Popular posts from this blog

De-obfuscating javascript code in Chrome Developer Tools

I had blogged about JavaScript debugging with Chrome Developer Tools  some time back, wherein I have explained how these developer tools can help in debugging javascript code. Today Google Chrome 12 was released and my Chrome browser was updated to this version. As with every release, there have been some improvements made on performance, usability etc,. One feature that stood out for me is the ability to De-obfuscate the javascript code. What is Minification? Minification is the process of removing unnecessary characters such as white spaces, comments, new lines from the source code. These otherwise would be added to make the code more readable. Minifying the source code helps in reducing the file size and thereby reducing the time taken to download the file. This is the reason why most of the popular javascript libraries such as jQuery are minified. A minified jQuery file is of 31 KB in size where as an uncompressed one is about 229 KB. Unfortunately, debugging minified javascript f
7 comments
Read more

Adding beforeRender and afterRender functions to a Backbone View

I was working on a Backbone application that updated the DOM when a response was received from the server. In a Backbone View, the initialize method would perform some operations and then call the render method to update the view. This worked fine, however there was scenario where in I wanted to perform some tasks before and after rendering the view. This can be considered as firing an event before and after the function had completed its execution. I found a very simple way to do this with Underscore's wrap method.
Post a Comment
Read more

On GraphQL and building an application using React Apollo

When I visualize building an application, I would think of using React and Redux on the front-end which talks to a set of RESTful services built with Node and Hapi (or Express). However, over a period of time, I've realized that this approach does not scale well when you add new features to the front-end. For example, consider a page that displays user information along with courses that a user has enrolled in. At a later point, you decide to add a section that displays popular book titles that one can view and purchase. If every entity is considered as a microservice then to get data from three different microservices would require three http  requests to be sent by the front-end app. The performance of the app would degrade with the increase in the number of http requests. I read about GraphQL and knew that it is an ideal way of building an app and I need not look forward to anything else. The GraphQL layer can be viewed as a facade which sits on top of your RESTful services o
Post a Comment
Read more