A.18. Chapter 18 Answers

Question 18-1

It’s necessary to write a function for creating new XMLHTTPRequest objects, because Microsoft browsers use two different methods of creating them, while all other major browsers use a third. By writing a function to test the browser in use, you can ensure that code will work on all major browsers.

Question 18-2

The purpose of the try...catch construct is to set an error trap for the code inside the try statement. If the code causes an error, the catch section will be executed instead of a general error being issued.

Question 18-3

An XMLHTTPRequest object has six properties and six methods (see Tables Table 18-1 and Table 18-2).

Question 18-4

You can tell that an Ajax call has completed when the readyState property of an object has a value of 4.

Question 18-5

When an Ajax call successfully completes, the object’s status will have a value of 200.

Question 18-6

The responseText property of an XMLHTTPRequest object contains the value returned by a successful Ajax call.

Question 18-7

The responseXML property of an XMLHTTPRequest object contains a DOM tree created from the XML returned by a successful Ajax call.

Question 18-8

To specify a callback function to handle Ajax responses, assign the function name to the XMLHTTPRequest object’s onreadystatechange property. You can also use an unnamed, inline function.

Question 18-9

To initiate an Ajax request, an XMLHTTPRequest object’s send method is called.

Question 18-10

The main differences between an Ajax GET and POST request are that GET requests append the data to the URL and not as a parameter of the send method, and POST requests pass the data as a parameter of the send method and require the correct form headers to be sent first.