javascript

CHAPTER 10 ■ SCRIPTING BOM
However, we receive this as a string:
"
"
So, we’re going to have to write a function to search through the string and create the , ,
, and Element nodes before we can place them on the page, making sure of course to get the
nesting right.
Because this is the final chapter in the book, you probably can roll a helper function to do the job by
yourself. So I’ll leave that, as they say, as an exercise for the reader.
Just kidding. You’d likely gnaw off a finger or two in frustration trying to code that.
It’d be pretty dull to explain, too. Turns out, I won’t have to.
Internet Explorer 4 gave every Element node a proprietary innerHTML member. If you assign a string
to innerHTML, JavaScript parses it into HTML and then replaces all descendents of the Element node with
that DOM branch. That may be draconian, but it’s practical, too. It’s so much so that Firefox, Safari, and
Opera have always implemented innerHTML, even though it’s not part of any DOM standard.
Anyway, innerHTML is totally perfect for parsing an HTML response, quietly converting it from a
string value to a branch of the DOM tree. I guess we’ll use it then.
Here’s how: XMLHttpRequest.responseText contains the string equivalent of the HTML in
data/s2.html. parseHTML() will assign that to innerHTML for . However, we’re
going to need to create that and the other elements of the scroller first with our helper function,
createElem()—but only if we received data/s2.html all right from the server or browser cache. To make
sure of that we test whether XMLHttpRequest.status is 200 (received data/s2.html from the server) or 304
(received data/s2.html from the cache).
With all those details spilling out of mind, let’s begin coding parseHTML() like so. Note that the req
parameter will contain the XMLHttpRequest object passed in by getData() when
XMLHttpRequest.readyState changes to 4:
function parseHTML(req) {
if (req.status === 200 || req.status === 304) {
}
}
Note that if you are testing this script on your computer, which is to say loading URLs with the
file:// protocol, there obviously will not be an http:// status code. So, XMLHttpRequest.status will
always be 0, no matter what. With this in mind, if you are testing the script on your computer, you must
replace 200 or 304 with 0. Otherwise, the if block will never run!
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