We Keep Coding

Starting a vbs script from a HTML file

I've been wrapping my head around this problem for a couple of days searching for all possible solutions on the forums and online but can't seem to get it working.
I'm calling a script by a link on a "button" to start a script on a server (in HTML):
<a href="#" onClick="RunScript();">
The script code is:
<script type="text/javascript" language="javascript">
function RunScript() {
var objShell = new ActiveXObject("WScript.Shell");
objShell.Run("%comspec% /k my_projects_EN.vbs" "), 1, false;
}
</script>
So why am I using a vbs? What I'm trying to do is create custom pages for each employee. So the vbs is actually checking the computer name and an if clause directs the employee to a custom page. With my basic knowledge of programming and a lot of hours of searching I did not find a better solution for this yet. So I'm trying to make this one to work.
And it does but only if I'm running the script locally (desktop). But as the webpage will be used in an intranet location this script will be on a server. And this is where it became a bit hairy as I can't seem to find the right combination of commands to do so. I already tried pushd for creating a mounted volume or currentDir for setting up the location of script but nothing seems to work completely.
I assume that I'm missing a subroutine for the function as adding anything there just stops the script - but how to go at it is beyond me.
All help is appreciated even if it means I have to bury myself into another program language (not preferred of course).
I am certain that there is a way to solve this other than sending a script to each employee to put on their desktop (each time a new employee comes to work).
Thanks
Edit: I see an additional clarification is in order:
We're creating an intranet webpage as a help for more efficient work for our employees. We're on the same level as the rest so not IT or admin rights guys so we're on our own.
The point is to have a personal page for each employee which can be accessed via the same interface. So a link has to send each person to another page that is why I've created the vbs code which helps with that. Checking several other options this seemed to be the simplest and best one - and it works at least partially. I don't see any security risks as all will be done on each client computer - the files themselves will be located on the server. The script itself does not represent any risk at least not that I would see it - but of course I'm not a specialist.
So in short this is what we're trying to do:
Main page -> link to My_projects button -> start script (located on the same server as the main page) -> determine the client computer name -> redirect to the right webpage.
Sorry for a lack of details, I see that it's sometimes hard to explain exactly what you want if you're not a pro in these things.
Thanks again.

If those computers are physically located at your workplace and you have control over the system, it would be better to tweak DNS redirections on those computers. Otherwise, more general and OS independent solution, would be session, cookie, or token on employee's computer. Still, some kind of authentication other than having one piece of machine, could be more versatile and secure (unless your PCs are 1000 feet underground :-) ).
Edit: What kind of info/data are sent to the server script? Server script runs on server and everything related to "this computer" (e.g. name) is actually referring to the server itself. Thus the script needs some data from the client to recognise his computer.

thanks for the effort
Everything is actually located on the server so the client computer only runs the page or interface which is in \Server\folder\folder for example.
In your browser you open the start page which contains a button with a link to this script (located on the same server).
When the script executes it searches for the computer name and send the user to his personal page:
Set wshShell = CreateObject( "WScript.Shell" )
strComputerName = wshShell.ExpandEnvironmentStrings( "%COMPUTERNAME%" )
On Error Resume Next
'#01 name_surname
If strComputerName = "XXXXXXXX" Then
CreateObject("WScript.Shell").Run """name_surname.html"""
and so on.
And this is all there is. As mentioned before we don't have admin rights to change anything on the client computer. So nothing is being done on the client side other that executing a script located on the server.

Html5 audio tag not working in Local IIS for Google translate_tts

Trying to use google's translate_tts as my fallback if the browser doesn't support speechSynthesis for my project.
Now I am having some trouble with getting the html5 audio working properly.
Been scratching my head and googling all day on why it wasn't working for me.
Then I came across some articles/forums saying that it's something to do with IIS. So I did a test code outside my site to see what happens, and was surprised this worked properly! But when using the same code in my original project which is running in IIS it doesn't work. AND it works when using IIS EXPRESS. I check the MIME types in IIS and mpeg and mp3 are there.
Even doing it in javascript doesn't work in IIS.
TextToSpeech.Audio = document.createElement("AUDIO");
TextToSpeech.Audio.src = url;
TextToSpeech.Audio.playbackRate = 1;
TextToSpeech.Audio.preload = 'auto';
TextToSpeech.Audio.volume = 1; // 0 to 1;
TextToSpeech.Audio.addEventListener('ended', function () {
//i have some code here...
});
TextToSpeech.Audio.addEventListener('error', function (error) { });
TextToSpeech.Audio.play();
Has anyone encountered this issue and happened to resolve it? Your help will be much appreciated, Thanks!
UPDATE: After some more googling, this might be because I am calling it from within my site hosted in IIS which has a proper hostname and my IIS Express runs the site in localhost:PORT which Google sees as noreferrer?

starting some time in the last few days, google seems to have placed a 'captcha' on this service and made it so that it can no longer be called by a server. so this may all be moot.
it used to be you could ONLY call it as a noreferrer, so i don't think noreferrer is your issue (or may be the least of your issues starting a few days back). one way to workaround the issue in fact was to add ref='noreferrer' to your link.
and this may be your initial issue: using wget, you had to use the -U Mozilla option which makes wget appear to be a browser. if you called the url without that, it didn't return anything. so if there is a way to make your IIS look like a browser when calling the google url, that may work.
this link google text-to-speech artile still does work in a browser, maybe that will help you use it the way you want.
however... starting july 28th, i get a '503 service not available' after using it for years with wget on my linux server. could be because it's metered and i've overrused it... i hope it comes back on. i only use it about 100x/day.
they always said it was 'not public' but it is widely used that way...
so that could be related if you're still trying to call it from IIS which i would think behaves similarly to calling it from a linux server.

Javascript running only once on Internet Explorer, runs properly when developer tools is open

We have an unusual problem with javascript running on IE 11. I tried it on one of our servers running IE8 and the same problem occurs. However, it runs fine on Chrome and Mozilla.
Here's the code in question:
SetGuideFatningCookie(fid); //set a cookie according to user choice
var validFatningCombo = ValidFatningCheck(); //ask server if user choice is valid using XMLHttpRequest GET request
if(validFatningCombo)
window.location.href = GetGuideTilbehoerURL(); //if valid redirect user to next page
else
popAutoSizeFancy("#GLfancy"); //if not show a fancybox with error text
The user chooses one of 7 choices. Then they click a button that runs the above code. The code sets a cookie containing the user's choice and asks the server if the choice is valid. If valid - we redirect the user and if not, we open a fancybox that contains some error text and two buttons - "Try again"(closes box and they can try again) and "Send us a message"(redirects user to our "ask us a question" page).
The code runs fine the first time the user goes to this process.
However, if they have chosen an invalid choice, they close the fancybox and try to choose another choice and continue -> then the fancy box appears ALWAYS, regardless of what the user chooses.
If they choose a valid choice and continue, get redirected to next page, then come back to this page and choose an invalid choice and press continue -> then they can continue to the next page without fancybox ever coming up.
However, if IE's developer tools are opened, the code runs correct every single time.
I have found many threads describing this is a problem with console.log. I have removed every single reference to console.log from all our .js files. It could be one of the external libraries that we are using, like jquery, modernizr, fancybox and menucool's tooltip library.
Therefore I tried including a console fallback function for IE, like this thread suggests:
Why does JavaScript only work after opening developer tools in IE once?
I am currently trying with this one, and I have tried every single other fallback console replacement from the thred I link to.
if (!window.console) window.console = {};
if (!window.console.log) window.console.log = function () { };
I tried including it:
Somewhere in our .js files
script element in head after loading all our .js files and all external libraries
script element in head before loading all our .js files and all external libraries
Inside $(document).ready(function() {}); , in a script element in head after loading all other js
So far, none of the fallback pieces of code I have tried in any of these 4 locations have solved the problem. It always behaves the same way in IE. I couldn't find another explanation than the "console" one for this problem so far, so if anyone got any insight on it, it would be greatly appreciated.
EDIT: I will include some more info:
The very act of opening Developer Tools removes the unwanted behaviour. No errors are ever shown in console.
I checked the server side to see if the server is getting the call from ValidFatningCheck(); It turns out that the call is made only the first time (or if Developer tools is open - every time) which is rather mysterious since the redirect/fancybox line comes after the server call and it doesn't fail to run, even if it runs wrong.
function ValidFatningCheck(){
var requestUrl = '/Tools.ashx?command=validscreen';
var req = new XMLHttpRequest();
req.open('GET', requestUrl, false);
req.send(null);
var res = "";
if (req.readyState==4)
res = req.responseText;
if(res == "true")
return true;
return false;
}
UPDATE : Problem solved by adding a timestamp to my XMLHttpRequest as multiple replies suggested. I didn't realize XMLHttpRequest uses AJAX so I overlooked it as a probable cause to the problem.

(I put in comments but will make this an answer now as it appears to have solved the problem) get requests are cached by IE but when the developer console is open it does not perform this cache.
three ways to fix:
add a timestamp to the request to trick the browser into thinking it is making a new request each time
var requestUrl = '/Tools.ashx?command=validscreen&time='+new Date().getTime();
set the response header to no-cache
make a POST request as these are not cached
(as pointed out by #juanmendes not ideal you are not editing a resource)

How to start two or more custom URL Protocol from Javascript

I have an old html page that creates a script file and executes it using:
fsoObject = new ActiveXObject("Scripting.FileSystemObject")
wshObject = new ActiveXObject("WScript.Shell")
I am trying to modify it and make it usable also from other browsers. If you know the answer stop reading and please answer. If there is no quick answer, here is the description of my attempts. I was successful in doing the job, but only when the script is shorter than 2000 characters. I need help for scripts longer than 2000 characters.
The webpage is for internal use only, so it is easy for me to create a custom URL protocol on each computer that runs a VBScript file from a network drive.
I created my custom URL Protocol that starts a VBScript file like this:
Windows Registry Editor Version 5.00
[HKEY_CLASSES_ROOT\MyUrlProtocol]
"URL Protocol"=""
#="Url:MyUrlProtocol"
"UseOriginalUrlEncoding"=dword:00000001
[HKEY_CLASSES_ROOT\MyUrlProtocol\DefaultIcon]
#="C:\\Windows\\System32\\WScript.exe"
[HKEY_CLASSES_ROOT\MyUrlProtocol\shell]
[HKEY_CLASSES_ROOT\MyUrlProtocol\shell\open]
[HKEY_CLASSES_ROOT\MyUrlProtocol\shell\open\command]
#="C:\\Windows\\System32\\WScript.exe \"X:\\MyUrlProtocol.vbs\" \"%1\""
In MyUrlProtocol.vbs I have this:
MsgBox "The length of the link is " & Len(WScript.Arguments(0)) & " characters"
MsgBox "The content of the link is: " & WScript.Arguments(0)
When I click on click me I see two messages, so everything works well (tested with Chrome and IE in Windows 7.)
It works also when I execute document.getElementById("test").click()
I thought this could be the solution: I would pass the text of the script to the VBS static script, which would create the dynamic script and run it, but with this system I can't pass more than ~2000 characters.
So I tried to split the text of the script in chunks smaller than 2000 characters and simulate several clicks on the link, but only the first one works.
So I tried with xmlhttp.open("GET","MyUrlProtocol:test",false);, but Chrome says Cross origin requests are only supported for HTTP.
Is it possible to pass more than 2000 characters to a VBScript script via a custom URL protocol?
If not, is it possible to call several custom URL protocols in sequence?
If not, is there another way to create a script file and run it from Javascript?
EDIT 1
I found a solution, but in Chrome only works when it likes, so I'm back to square one.
The code below in IE executes the script 4 times (correct), but in Chrome only the first execution runs.
If I change it to delay += 2000, then Chrome usually runs the script 2 times, but sometimes 1 and sometimes 3 or even 4 times.
If I change it to delay += 10000, then it usually runs the script 4 times, but sometimes misses one.
The function is always executed 4 times, both in Chrome and IE. What is weird is that the sr.click() sometimes does nothing and the function execution continues.
<HTML>
<HEAD>
<script>
var delay;
function runScript(text) {
setTimeout(function(){runScript2(text)}, delay);
delay += 100;
}
function runScript2(text) {
var sr = document.getElementById('scriptRunner');
sr.href='intelliclad:'+text;
sr.click();
}
function test(){
delay = 0;
runScript("uno");
runScript("due");
runScript("tre");
runScript("quattro");
}
</script>
</HEAD>
<BODY>
<input type="button" value="Run test" onclick="test()">
scriptRunner
</BODY>
</HMTL>
EDIT 2
I tried with Luke's suggestion of setting the next timeout from inside the call back but nothing changed (IE works always, Chrome whenever it likes).
Here is the new code:
var scripts;
var delay = 2000;
function runScript() {
var sr = document.getElementById('scriptRunner');
sr.href = 'intelliclad:' + scripts.shift();
sr.click();
if(scripts.length)
setTimeout(function() {runScript()}, delay);
}
function test(){
scripts = ["uno", "due", "tre", "quattro"];
runScript();
}
Some background: The page asks for the shape of a panel, which can be just a few parameters [nfaces=1, shape1='square', width1=100] or hundreds of parameters for panels with many faces, many slots, many fasteners, etc. After asking for all the parameters a script for our internal 3D CAD (which can be larger than 20KB) is generated and the CAD is started and asked to execute the script.
I would like to do all on the client side, because the page is served by a Domino web server, which can't even dream of managing such a complex script.

I didn't read your whole post...have an answer:
I too wish that custom url protocols can handle long urls. They simply do not. IE is even worse as some OSs only accept 800 chars.
So, here's the solution:
For long urls, only pass a single use token. The vbscript uses the token
and does a url get to your web server to get all of the data.
This is the only way I've been able to successfully pass lots of data around. If you ever find a clearer solution, please remember to post it here.
Update:
Note that this is the best way I have found to deal with the url protocol limitations. I too wish this was not necessary. This does work and works well.
You mentioned Dominos, so possibly you need something in a POS environment... I create a web based POS system, so we could face a lot of the same issues.
Suppose you want a custom url to print a pdf to the default printer without the annoying popup window. We need to do this thousands of times a day...
When building the web page, add the print button which when pressed calls the custom url: myproto://printpdf?id=12345&tocken=onetimetoken
this will execute your vbscript on the local desktop
in your vbscript, parse the arguments and react. In this case, your command is printpdf and the id is 123456 and you have a onetime tocken key.
have the vb script to an https get to: https://mydomain.com/APIs/printpdf.whatever?id=12345&key=onetimetoken
check the credentials based on the ip address and token, if all aligns, then return the contents of the pdf (you may want to convert the pdf to a byte array string)
now the vbscript has the pdf, assemble it and write it to a temp folder then execute a silent pdf print command (I use Sumatra PDF http://blog.kowalczyk.info/software/sumatrapdf/free-pdf-reader.html)
mission accomplished.
Since I do know what you what to do in your custom url and the general workflow, I can only describe how I've solved the sort url issue.
Using this technique, the possibilities are limitless. You have full control over the local computer running the web browser, you have a onetime use token which grants access to a web API with can return any sort of information you program.
You could write a custom url protocol to turn on the pizza oven if you wanted :)
If you are not able to create the server side code which is listening for vbscript's get request then this would not work.
You might be able to pass the data from the browser to the vbscript using the clipboard.
Update 2:
Since in this case the data is on the client (one single form can define hundreds of parameters), the server API doesn't know what to answer to the vb script request. So the workflow described above must be preceded by these two steps:
The onkeypress event executes a submit to send the current parameters to the server
The server replies with the refreshed form, adding to the body onload a call to a function which uses another submit to call the custom url, as described on point 1 listed above.
Update 3:
stenci, what you've added (in Update 2) will work. I would do it like this:
user presses a button saying I'm done editing the form
ajax post the form to the server
the server saves the data and attaches unique key to the datastore
the server returns the key to ajax callback function
now the client has a single use key and invokes the url schema passing the key
vbscript does an https get to the server and passes the key
server returns the data to the vbscript
It is a bit long winded. Once coded it will work like a charm.
The only other alternative I can see is to copy the form data to the clipboard using something like: http://zeroclipboard.org/
and then in vbscript see if you can read the clipboard like: Use clipboard from VBScript

How about creating an iFrame for each instance?
Something like this:
function runScript(text) {
var iframe = document.createElement('iframe');
iframe.src = 'intelliclad:'+text;
document.body.appendChild(iframe);
}
function test(){
runScript("uno");
runScript("due");
runScript("tre");
runScript("quattro");
}
You can then use css styling to make these iframes transparent / hidden.

You might not like this answer, but I've used this method in the past and it works.
Instead of relying on ActiveX, consider using a Java Applet, and JNI.
Basically, you have to make sure the native scripts you want to run are available on your client machine, along with a JNI wrapper.
The applet will have to be at least self signed, for the browser to allow it to load and access a native library. Once the JNI libraries are loaded, you can easily call methods from the page / applet.
As a consequence of using Java, you could possibly use the same applet for windows as well as linux clients, provided of course you have native libraries present on the respective clients.
This series of articles talks about precisely your problem : http://www.javaworld.com/article/2076775/java-security/escape-the-sandbox--access-native-methods-from-an-applet.html
P.S the article is really old, but the concept remains unchanged.

"undefined" randomly appended in 1% of requested urls on my website since 12 june 2012

Since 12 june 2012 11:20 TU, I see very weirds errors in my varnish/apache logs.
Sometimes, when a user has requested one page, several seconds later I see a similar request but the all string after the last / in the url has been replaced by "undefined".
Example:
http://example.com/foo/bar triggers a http://example.com/foo/undefined request.
Of course theses "undefined" pages does not exist and my 404 page is returned instead (which is a custom page with a standard layout, not a classic apache 404)
This happens with any pages (from the homepage to the deepest)
with various browsers, (mostly Chrome 19, but also firefox 3.5 to 12, IE 8/9...) but only 1% of the trafic.
The headers sent by these request are classic headers (and there is no ajax headers).
For a given ip, this seems occur randomly: sometimes at the first page visited, sometimes on a random page during the visit, sometimes several pages during the visit...
Of course it looks like a javascript problem (I'm using jquery 1.7.2 hosted by google), but I've absolutely nothing changed in the js/html or the server configuration since several days and I never saw this kind of error before. And of course, there is no such links in the html.
I also noticed some interesting facts:
the undefined requests are never found as referer of another pages, but instead the "real" pages were used as referer for the following request of the same IP (the user has the ability to use the classic menu on the 404 page)
I did not see any trace of these pages in Google Analytics, so I assume no javascript has been executed (tracker exists on all pages including 404)
nobody has contacted us about this, even when I invoked the problem in the social networks of the website
most of the users continue the visit after that
All theses facts make me think the problem occurs silently in the browers, probably triggered by a buggy add-on, antivirus, a browser bar or a crappy manufacturer soft integrated in browsers updated yesterday (but I didn't find any add-on released yesterday for chrome, firefox and IE).
Is anyone here has noticed the same issue, or have a more complete explanation?

There is no simple straight answer.
You are going to have to debug this and it is probably JavaScript due to the 'undefined' word in the URL. However it doesn't have to be AJAX, it could be JavaScript creating any URL that is automatically resolved by the browser (e.g. JavaScript that sets the src attribute on an image tag, setting a css-image attribute, etc). I use Firefox with Firebug installed most of the time, so my directions will be with that in mind.
Firebug Initial Setup
Skip this if you already know how to use Firebug.
After the installs and restarting Firefox for Firebug, you are going to have to enable most of Firebug's 'panels'. To open Firebug there will be a little fire bug/insect looking thing in the top right corner of your browser or you can press F12. Click through the Firebug tabs 'Console', 'Script', 'Net' and enable them by opening them up and reading the panel's information. You might have to refresh the page to get them working properly.
Debugging User Interaction
Navigate to one of the pages that has the issue with Firebug open and the Net panel active. In the Net panel there will be a few options: 'Clear', 'Persist', 'All', 'Html', etc. Make sure ALL is selected. Don't do anything on the page and try not to mouse over anything on it. Look through the requests. The request for the invalid URL will be red and probably have a status of 404 Not Found (or similar).
See it on load? Skip to the next part.
Don't see it on initial load? Start using your page and continue here.
Start clicking on every feature, mouse over everything, etc. Keep your eyes on the Net panel and watch for a requests that fail. You might have to be creative, but continue using your application till you see your browser make an invalid request. If the page makes many requests, feel free to hit the 'Clear' button on the top left of the Net panel to clear it up a bit.
If you submit the page and see a failed request go out really quick but then lose it because the next page loads, enable persistence by clicking 'Persist' in the top left of the Net panel.
Once it does, and it should, consider what you did to make that happen. See if you can make it happen again. After you figure out what user interaction is making it happen, dive into that code and start looking for things that are making invalid requests.
You can use the Script tab to setup breakpoints in your JavaScript and step through them. Investigate event handlers done via $(elemment).bind/click/focus/etc or from old school event attributes like onclick=""/onfocus="" etc.
If the request is happening as soon as the page loads
This is going to be a little harder to peg down. You will need to go to the Script tab and start adding break points to every script that runs on load. You do this by clicking on the left side of the line of JavaScript.
Reload your page and your break points should stop the browser from loading the page. Press the 'Continue' button on the script panel. Go to your net panel and see if your request was made, continue till it is found. You can use this to narrow down where the request is being made from by slowly adding more and more break points and then stepping into and out of functions.
What you are looking for in your code
Something that is similar to the following:
var url = workingUrl + someObject['someProperty'];
var url = workingUrl + someObject.someProperty;
Keep in mind that someObject might be an object {}, an array [], or any of the internal browser types. The point is that a property will be accessed that doesn't exist.
I don't see any 404/red requests
Then whatever is causing it isn't being triggered by your tests. Try using more things. The point is you should be able to make the request happen somehow. You just don't know yet. It has to show up in the Net panel. The only time it won't is when you aren't doing whatever triggers it.
Conclusion
There is no super easy way to peg down what exactly is going on. However using the methods I outlined you should be at least be able to get close. It is probably something you aren't even considering.

Based on this post, I reverse-engineered the "Complitly" Chrome Plugin/malware, and found that this extension is injecting an "improved autocomplete" feature that was throwing "undefined" requests at every site that has a input text field with NAME or ID of "search", "q" and many others.
I found also that the enable.js file (one of complitly files) were checking a global variable called "suggestmeyes_loaded" to see if it's already loaded (like a Singleton). So, setting this variable to false disables the plugin.
To disable the malware and stop "undefined" requests, apply this to every page with a search field on your site:
<script type="text/javascript">
window.suggestmeyes_loaded = true;
</script>
This malware also redirects your users to a "searchcompletion.com" site, sometimes showing competitors ADS. So, it should be taken seriously.

You have correctly established that the undefined relates to a JavaScript problem and if your site users haven't complained about seeing error pages, you could check the following.
If JavaScript is used to set or change image locations, it sometimes happens that an undefined makes its way into the URI.
When that happens, the browser will happily try to load the image (no AJAX headers), but it will leave hints: it sets a particular Accept: header; instead of text/html, text/xml, ... it will use image/jpeg, image/png, ....
Once such a header is confirmed, you have narrowed down the problem to images only. Finding the root cause will possibly take some time though :)
Update
To help debugging you could override $.fn.attr() and invoke the debugger when something is being assigned to undefined. Something like this:
​(function($, undefined) {
var $attr = $.fn.attr;
$.fn.attr = function(attributeName, value) {
var v = attributeName === 'src' ? value : attributeName.src;
if (v === 'undefined') {
alert("Setting src to undefined");
}
return $attr(attributeName, value);
}
}(jQuery));

Some facts that have been established, especially in this thread: http://productforums.google.com/forum/#!msg/chrome/G1snYHaHSOc/p8RLCohxz2kJ
it happens on pages that have no javascript at all.
this proves that it is not an on-page programming error
the user is unaware of the issue and continues to browse quite happily.
it happens a few seconds after the person visits the page.
it doesn't happen to everybody.
happens on multiple browsers (Chrome, IE, Firefox, Mobile Safari, Opera)
happens on multiple operating systems (Linux, Android, NT)
happens on multiple web servers (IIS, Nginx, Apache)
I have one case of googlebot following the link and claiming the same referrer. They may just be trying to be clever and the browser communicated it to the mothership who then set out a bot to investigate.
I am fairly convinced by the proposal that it is caused by plugins. Complitly is one, but that doesn't support Opera. There many be others.
Though the mobile browsers weigh against the plugin theory.
Sysadmins have reported a major drop off by adding some javascript on the page to trick Complitly into thinking it is already initialized.
Here's my solution for nginx:
location ~ undefined/?$ {
return 204;
}
This returns "yeah okay, but no content for you".
If you are on website.com/some/page and you (somehow) navigate to website.com/some/page/undefined the browser will show the URL as changed but will not even do a page reload. The previous page will stay as it was in the window.
If for some reason this is something experienced by users then they will have a clean noop experience and it will not disturb whatever they were doing.

This sounds like a race condition where a variable is not getting properly initialized before getting used. Considering this is not an AJAX issue according to your comments, there will be a couple of ways of figuring this out, listed below.
Hookup a Javascript exception Logger: this will help you catch just about all random javascript exceptions in your log. Most of the time programmatic errors will bubble up here. Put it before any scripts. You will need to catch these on the server and print them to your logs for analysis later. This is your first line of defense. Here is an example:
window.onerror = function(m,f,l) {
var e = window.encodeURIComponent;
new Image().src = "/jslog?msg=" + e(m) + "&filename=" + e(f) + "&line=" + e(l) + "&url=" + e(window.location.href);
};
Search for window.location: for each of these instances you should add logging or check for undefined concats/appenders to your window.location. For example:
function myCode(loc) {
// window.location.href = loc; // old
typeof loc === 'undefined' && window.onerror(...); //new
window.location.href = loc; //new
}
or the slightly cleaner:
window.setLocation = function(url) {
/undefined/.test(url) ?
window.onerror(...) : window.location.href = url;
}
function myCode(loc) {
//window.location.href = loc; //old
window.setLocation(loc); //new
}
If you are interested in getting stacktraces at this stage take a look at: https://github.com/eriwen/javascript-stacktrace
Grab all unhandled undefined links: Besides window.location The only thing left are the DOM links themselves. The third step is to check all unhandeled DOM links for your invalid URL pattern (you can attach this right after jQuery finishes loading, earlier better):
$("body").on("click", "a[href$='undefined']", function() {
window.onerror('Bad link: ' + $(this).html()); //alert home base
});
Hope this is helpful. Happy debugging.

I'm wondering if this might be an adblocker issue. When I search through the logs by IP address it appears that every request by a particular user to /folder/page.html is followed by a request to /folder/undefined

I don't know if this helps, but my website is replacing one particular *.webp image file with undefined after it's loaded in multiple browsers. Is your site hosting webp images?

I had a similar problem (but with /null 404 errors in the console) that #andrew-martinez's answer helped me to resolve.
Turns out that I was using img tags with an empty src field:
<img src="" alt="My image" data-src="/images/my-image.jpg">
My idea was to prevent browser from loading the image at page load to manually load later by setting the src attribute from the data-src attribute with javascript (lazy loading). But when combined with iDangerous Swiper, that method caused the error.