HTML and CSS Reference
In-Depth Information
12.3.1 The First Test
The very first test we will write is the one that expects an XMLHttpRequest object.
As outlined in Section 12.2.2, Choosing the Interface Style, the properties we rely
on are the open and send methods. The onreadystatechange handler needs
the readyState property to know when the request has finished. Last, but not
least, we will eventually need the setRequestHeader method in order to, well,
set request headers.
Listing 12.3 shows the test in full; save it in test/ajax _ test.js .
Listing 12.3 Testing for an XMLHttpRequest object
TestCase("AjaxCreateTest", {
"test should return XMLHttpRequest object": function () {
var xhr = tddjs.ajax.create();
assert(tddjs.isHostMethod(xhr, "open"));
assert(tddjs.isHostMethod(xhr, "send"));
assert(tddjs.isHostMethod(xhr, "setRequestHeader"));
This test fails as expected because there is no tddjs.ajax namespace.
Listing 12.4 shows the namespace declaration that goes in src/ajax.js . In order
for this to run, the tddjs.namespace method from Chapter 6, Applied Functions
and Closures, needs to be available in lib/tdd.js .
Listing 12.4 Creating the ajax namespace
With this in place the test fails in response to the missing create method. We
will need a little background before we can implement it.
12.3.2 XMLHttpRequest Background
Microsoft invented XMLHttpRequest as an ActiveX object back in 1999. Com-
petitors followed suit shortly after, and today the object is available in just about
every current browser. It's even on its way to becoming a W3C standard, in Last
Call Working Draft at the time of writing. Listing 12.5 shows how the object is
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