Injecting JavaScript into head element of website using Fiddler
I was thinking of using Fiddler for the following purpose...
I have a JavaScript based service I want to demonstrate to potential clients. In order to show them what their website could look like if they install (i.e. include) my script, I want to set up Fiddler on my PC, so that when fetching the client's website, the
<script type="text/JavaScript" src="myscript.js"></script>
line will be included in the HTML <head> section.
Can this be easily done with Fiddler? Could someone point me to where I may find the documentation covering that, if it is?
Thanks!
----Update----
For the time being I have resorted to using a BHO to add my script to the page. I use execScript(), upon onDocumentComplete, to run a simple piece of JavaScript which appends the .js file I need to the page. But EricLaw's pointers and jitter's answer seem like the way to go for a more complete (and elegant) way to do what I need.
If someone is interested I could upload the BHO code here. -Thanks!
Answer
Open fiddler -> Menu Rules -> Customize Rules (or hit Ctrl+R)
The CustomRule.js file opens. Scroll down until you find the line
static function OnBeforeResponse(oSession: Session)
This is where your code goes. Here you can change the server response before the browser sees it.
The following code sample shows how to include a custom piece of jQuery code which replaces the Unanswered link in the horizontal menu with a link which serves as short cut to Unanswered jQuery Questions
I first show you the jQuery code I want to include
<script type='text/javascript'>
$(function() {
var newLink = '<a href="/unanswered/tagged/jquery">Unanswered jQuery</a>';
$('div#hmenus div.nav:first ul li:last a').replaceWith(newLink);
});
</script>
Now the fiddler code (based on code found in CustomRules.js and code samples from the FiddlerScript CookBook)
//is it a html-response and is it from stackoverflow.com
if (oSession.oResponse.headers.ExistsAndContains("Content-Type", "html") &&
oSession.HostnameIs("stackoverflow.com")) {
// Remove any compression or chunking
oSession.utilDecodeResponse();
var oBody = System.Text.Encoding.UTF8.GetString(oSession.responseBodyBytes);
// Match the jQuery script tag
var oRegEx = /(<script[^>]*jquery.min.js"><\/script>)/gi;
// replace the script tag withitself (no change) + append custom script tag
oBody = oBody.replace(oRegEx, "$1<script type='text/javascript'>$(function() {$('div#hmenus div.nav:first ul li:last a').replaceWith('<a href=\"/unanswered/tagged/jquery\">Unanswered jQuery</a>');})</script>");
// Set the response body to the changed body string
oSession.utilSetResponseBody(oBody);
}
I think you should now able to hackyourself together a piece of code which fits your problem.
Example
// Match the head end
var oRegEx = /(<\/head>)/gi;
// replace with new script
oBody = oBody.replace(oRegEx, "<script type='text/javascript' src='http://url/myscript.js'></script>$1");