That first attempt worked great – while it was included in a page from the same server that provided the shipping quote. The first time I tried to include it as a widget on this blog, it failed. According to the Inspect Element facility in Chromium, the problem is:
Uncaught Error: NETWORK_ERR: XMLHttpRequest Exception 101
when the send() function was invoked on the XMLHttpRequest object. At the same point Firefox says
Error: uncaught exception: [Exception… “Component returned failure code: 0x80004005 (NS_ERROR_FAILURE) [nsIXMLHttpRequest.send]” nsresult: “0x80004005 (NS_ERROR_FAILURE)” location: “JS frame :: http://localhost:22791/static/js/posmalaysia5.js :: pos_spider_box_quote :: line 26” data: no]
And in IE8 the debugger tells me (on the open() method of XmlHttpRequest)
Breaking on JScript runtime error – Access is denied
The request is received by my server from Firefox and Chromium, but not from IE8 (obviously, I suppose, if it’s failing on the open() method).
The Internet told me I was attempting Cross-domain scripting and it’s impossible unless you use version 4.8 of Firefox, pretend you’ve fixed it by using a proxy server, or defeat impossibility by using jQuery, flxHR or some other library whose developers presumably don’t understand the word ‘impossible’.
I decided that either this bloody thing is impossible or it isn’t, and that if it isn’t, why should I need a library to do what I wanted to do? For my specific application (or any I can currently imagine I might want to implement) I just want to exchange a very few items of data. If there is a way of doing it, how complex does it have to be?
Anyway, I didn’t have clue a couple of days ago, so I started with what seemed to me to be an unusually straightforward article on cross-domain scripting at IBM:
A quick read of the document led me to think that JSON wasn’t all that bad. If it solved my problem, I could probably bring myself to use it. The article ‘goes off on one’ about jQuery in the later stages, but I decided I would cross that domain when I came to it. I was of the opinion that JSON alone would give me what I want.
The script creates the widget content. It also sets a var – which I’m guessing has some sort of global scope as it’s outside a function block – to the DIV which will hold the ‘result’ of a shipping quotation.
A text INPUT box and a SELECT element in the widget both have onchange() methods which call a function that’s part of the widget download. In the function called by onchange(), I assemble an URL from the values in the inputbox and the select element, to create a SCRIPT element in the document’s HEAD with the constructed URL as its SRC attribute.
Here’s an example of the URL I use as the SRC attribute of the SCRIPT element the widget code creates in the document’s HEAD:
pos_spider_box_quotes.innerHTML = ‘RM60.00 <i>Pos Laju Document</i><br>RM75.00 <i>Pos Laju Parcel</i>’;
See? Just a bare assignment to the var I prepared earlier. And lo and behold, the results are set in the widget! What is ‘impossible’ about that?