Showing posts with label Ajax. Show all posts
Showing posts with label Ajax. Show all posts

Oct 12, 2012

Backbone.js - Parsing the response from the server

From past few weeks, I've been learning Backbone.js in great detail and I think it's a great framework that helps you modularize your code easily. Last week I wrote about 'Model validation in constructor' and then started to look at Collections in Backbone. The Model objects can be viewed as table rows and the Collection as a table. A Collection can declare the model property and indicate what kind of data it will hold. I was looking into ways in which a Collection can be populated by fetching the model data from the server. One way to do that is to ask the Model to fetch the data and then add the response to the Collection. The other way of doing this is to fetch the Collection data directly from the server i.e. instead of defining a Model you create a Collection by fetching the data from the server. Usually when you send a request to the server, the response data is essentially a collection of objects. In this case you really don't need a Model to be defined.

Sep 24, 2012

Pushing Ajax responses using Observer Pattern in JavaScript

Last week I'd played around with couple of design patterns in JavaScript (Constructor and Module pattern). I really liked the Module pattern i.e. the approach taken in JavaScript to enable encapsulation of data in a Class (functions in JavaScript). I was building an application using these Design patterns but found that making Ajax request inside a function in a module was not the right approach. JavaScript would send a request and start executing the next statement. I wanted to use an approach that would push the data from the Model whenever there was some new data available. This lead me to try the 'Observer pattern' in JavaScript.

Aug 13, 2012

Uploading chunks of a large file using XHR2

I was having a conversation with my college friend about the enhancements in XHR2 and I was showing him how one can upload a file to the server using plain Ajax. He asked me whether I can upload a large file to the server such as a video file. I tried doing that but was bumped when the server reported with 400 error telling me that the 'POST size has exceeded maximum limit'. This got me thinking whether I can upload chunks of a large file to the server. I referred to the FileSystem API and came across the slice method that allows you to get a fragment of a file.

Jul 7, 2011

Submitting Form using FormData object in HTML5 using XmlHttpRequest Level 2

The other day I had posted on uploading a file using XmlHttpRequest 2 and tracking the progress of the file upload process using the progress event on XHR2 object and the progress tag. Another enhancement added to the XHR2 specification is the introduction of FormData object. Using the FormData object, one can create a set of key-value pairs and send them as form data in a XHR request. The FormData object is passed in the send() method of the XHR object:

Apr 21, 2011

HTML5 XmlHttpRequest 2 v/s Flash\Silverlight approach to cross-origin requests

A few days back I had posted on XmlHttpRequest Level 2, describing how cross-origin requests can be achieved. A few folks on my team asked me how different it is from Flash\Silverlight's approach to achieve cross domain request\response with crossdomain.xml. The approach that these plugins take to send a request and receive a response is completely different from that of XmlHttpRequest's approach.

Apr 18, 2011

HTML5 XmlHttpRequest 2 - Cross origin request

HTML5 specification has introduced a few enhancements for XmlHttpRequest object and one of them is the ability to make cross-origin request. That is, a host can send a XmlHttpRequest request to another host and receive a response in return. On the server-side, a check can be made to see whether the request can be accepted from the given origin. In this post I'll try to explain how this can be done using ColdFusion.

Client side:

On the client side, a XmlHttpRequest object is created and then a GET request is made to the remote server.

 var client = new XMLHttpRequest();  
client.onreadystatechange = readyStateChangeHandler;  
client.open("GET","http://{remote-address}/{path-to-file}.cfm",true);  
client.send();       

For example, say example.com wants to get a response from another domain say abc.com, then as observed from the above code the request would look like:


client.open("GET","http://abc.com/dir1/foo.cfm",true);  

Server side:

When a request is sent to the server, the request header would contain a key ORIGIN whose value will be the domain name from which the request was made. In this case the value would be example.com. The server side code can then perform a check to see whether the request origin belongs to the list of origins from which the request can be accepted.

 <cfif structKeyExists(getHTTPRequestData().headers,"origin") >   
    <cfset origin = getHTTPRequestData().headers.origin />   
    <cfif origin eq "http://example.com">   
      <cfheader name="Access-Control-Allow-Origin"   
         value="http://example.com">   
      <cfoutput>#timeFormat(now(),"medium")#</cfoutput>   
    </cfif>   
 </cfif>   
As seen from the above code, the response header ACCESS-CONTROL-ALLOW-ORIGIN is set to allow cross-origin requests from example.com. This now enables requests from example.com to be served from abc.com. 



Jan 8, 2011

Server sent events with HTML5 and ColdFusion

There are several ways to interact with the server apart from the traditional request\response and refresh all protocol. They are polling, long polling, Ajax and Websockets (pusherapp). Of all these Ajax and Websockets have been very popular. There is another way to interact with the server such that the server can send notifications to the client using Server Sent Events (SSE). SSE is a part of HTML5 spec: http://dev.w3.org/html5/eventsource/