Peter Lubbers - Pro HTML 5 Programming

“SEEMINGLY ARBITRARY” TIMES
CHAPTER 5 ■ USING THE COMMUNICATION APIS
In the XMLHttpRequest Level 2 specification’s description for the readystatechange event (maintained for
backward compatibility), the readyState attribute is described as changing at, get this, “some seemingly
arbitrary times for historical reasons.”
Browser Support for HTML5 XMLHttpRequest Level 2
As shown in Table 5-3, HTML5 XMLHttpRequest is already supported in many browsers at the time of
this writing.
Table 5-3. Browser support for HTML5 XMLHttpRequest
Browser Details
Chrome Supported in version 2.0 and greater
Firefox Supported in version 3.5 and greater
Internet Explorer Not supported
Opera Not supported
Safari Supported in version 4.0 and greater
Due to the varying levels of support, it is a good idea to first test if HTML5 XMLHttpRequest is
supported, before you use these elements. The section “Checking for Browser Support” later in this
chapter will show you how you can programmatically check for browser support.
Using the XMLHttpRequest API
In this section, we’ll explore the use of the XMLHttpRequest in more detail. For the sake of illustration,
we’ve created a simple HTML page—crossOriginUpload.html. The sample code for the following
examples is located in the code/communication folder.
Checking for Browser Support
Before you try to use XMLHttpRequest Level 2 functionality—such as cross-origin support—it is a good
idea to check if it is supported. You can do this by checking whether the new withCredentials property is
available on an XMLHttpRequest object as shown in Listing 5-7.
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