HTML and CSS Reference
In-Depth Information
This code shows a JavaScript function—
GetOrders()
—intended to retrieve order data for a specific
customer from the SQL Server. The
GetOrders()
function accepts a customer ID whose orders are to be
retrieved.
Inside, the function creates a new instance of
XMLHttpRequest
. The
open()
method of the
XMLHttpRequest
object opens a communication channel with a remote request. The first parameter of the
open()
method is the type of request (GET/POST) being made, and the second parameter is the location of
the remote resource. In this example, a POST request is made to an MVC action method named
GetOrders
.
The
XMLHttpRequest
object's
setRequestHeader()
method sets the MIME content type of the request to
application/json
.
The
XMLHttpRequest
object raises the
onreadystatechange
event when the state of the request changes.
The
onreadystatechange
event-handler function checks the
readyState
property of the
XMLHttpRequest
object. The
readyState
object indicates the current state of the request and can have values from
0
to
4
. A
value of
4
indicates that the request is completed. If the request is completed, you can use the
postMessage()
method to send the data returned by the remote resource back to the web page. The
responseText
property of the
XMLHttpRequest
object returns the response from the remote resource. In this
case, the MVC action method is assumed to return data in JSON format, and hence
responseText
is sent
directly to the web page.
To initiate the request, you need to call the
XMLHttpRequest
object's
send()
method.
send()
takes
request parameters, if any. Because you wish to send request data in JSON format, you convert the
customer ID to a JSON object and then pass it as a parameter to
send()
.
Using Web Workers That Require Server-side Data
In this final example, you develop an ASP.NET MVC application that uses web workers to fetch data from
the server and display it in a view. The main view of the application is shown in Figure 10-8.
Figure 10-8.
Order History application
