Answers to Exercises - Beginning JavaScript - page 647

fpCallback(tempRequest.responseText);
}
else
{
alert(“An error occurred while attempting to “ +
“contact the server.”);
}
}
}
this.request.onreadystatechange = request_readystatechange;
}
this.request.send(null);
if (!this.async)
{
this.callBack(this.request.responseText);
}
}
This new code fi nishes off the method. Starting with the fi rst if block, a new variable called fpCallback
is assigned the value of this.callBack . This is done for the same reasons as with the tempRequest
variable — scoping issues — as this points to the request_readystatechange() function instead
of the HttpRequest object. Other than this change, the asynchronous code remains the same. The
request_readystatechange() function handles the readystatechange event and calls the call-
back function when the request is successful.
The second if block is much simpler. Because this code executes only if synchronous communica-
tion is desired, all you have to do is call the callback function and pass the XMLHttpRequest object's
responseText property.
Using this newly refactored module is quite simple. The following code makes an asynchronous
request for a fi ctitious text fi le called test.txt .
function request_callback(sResponseText)
{
alert(sResponseText);
}
var oHttp = new HttpRequest(“test.txt”, request_callback);
oHttp.send();
Nothing has really changed for asynchronous requests. This is the exact same code used earlier in the
chapter. If you want to use synchronous communication, simply set async to false , like this:
function request_callback(sResponseText)
{
alert(sResponseText);
}
var oHttp = new HttpRequest(“test.txt”, request_callback);