We Keep Coding

Cannot get reference to one page from another

I am working on a web app that needs to have two parts. The one is a controller and the other is a display. Something like Google Slides in presentation mode. The controller has a button to launch the display:
<script language="JavaScript">
function OpenMain()
{
var MainPage = window.open("TheUltraSignalLite.html");
TimerIMG = MainPage.document.getElementById("TimerIMG");
TimerIMG.src = "TM-Full-Blue.jpg";
}
</Script>
The call to window.open seems to return null. I have tried Chrome, Edge, Firefox, and Opera and they all have the result. These are all local files for now, but I might put in on a web server someday. I have seen some answers that want you to turn off security, but I cannot ask everyone who uses this app to turn off security. How do I get a valid reference to the display window?
Edit 1:
Yes, window.open from the local disk does cause a CORS restriction.
I tried this where both files are in the same AWS S3 Bucket, so the CORS should not be an issue. But I still get a null on the window.open. If I put a breakpoint on the first line, then everything worked. If I split the open and the rest of the code into two functions with two buttons, it works. So it looks like I have to find a way to run the open in an async way.
Edit 2
My solution to keep it simple was to put the window.open in the OnLoad event. This opens the child window and allows it to fully render and the value of MainPage is ready to use. (I changed the MainPage to a global variable.) I still have to run it from some type of web server, rather than loacl file, but that is not a big deal.

If you are not allowed to access the new window content, then the problem you are encountering is a basic security feature of web browsers. Citing mdn:
The returned reference can be used to access properties and methods of the new window as long as it complies with Same-origin policy security requirements
To read more about Same-origin policy
If your new window respects the Same-origin policy, then you can access the content of the new window with for example:
// Open index.html from the current origin
const newWindow = window.open('index.html')
const h1 = newWindow.document.querySelector('h1')
If you want to avoid asking users for pop-up permission, then you should probably use a link instead of a pop-up.

javascript link window open without extra slash

Let's say I am currently at the following link:
"localhost/admin/test" when i do
window.open("/user/list/2034", "_blank")
it will appear like this:
localhost/admin/test/user/list/2034
what can i do to make it like this instead?
localhost/user/list/2034

I am assuming that windows should be window. If it really is windows then you have a custom object and need to show us what that is before we can answer your question.
The other point to note is that window.open will open a new window, regardless what you name it, so you don't need to use the _blank name. You only need to specify a name if you want to subsequently reuse that window (e.g. open another URL in the same other window).
When at http://localhost/admin/test, if you do:
window.open("/user/list/2034")
It will go to http://localhost/user/list/2034, unless...
window.open has been redefined somewhere. You can do console.log(window.open) and the console should say something like ƒ open() { [native code] } if it hasn't been redefined.
Your web server is responding to /user/list/2034 with a redirect to /admin/test/user/list/2034. The network tab in your developer console will show you the HTTP requests and responses where you can see if the web server is redirecting.
Your link really doesn't start with a / and you actually have window.open("user/list/2034")
You're viewing a cached version of the page with the above error in it, the source code is fixed but the browser hasn't loaded it. Try again in a private browsing window to see if it still happens.
You have some browser plug-in or extension interfering with your page. Try another browser/computer without the extensions and see if it still happens.

HTML transient modal window

We have a legacy web application. At various places it opens a window with the help of Privilege Manager on Firefox to get the needed result.
Some of these windows open a Java applet or a PDF document.
The client machines are updating Firefox and Privilege Manager is gone.
What is the easiest way around it?
The problems are :
There must be only one instance of the pop-up at anyone time. This could be done by selecting appropriate window name on window.open() call.
If the window is opened again (by means of user action), it should not reload but just focus to bring it to the foreground (I have seen I can keep a reference to the window on JavaScript to do that)
It basically really must be transient/modal so that the client cannot leave the current page or reload or any other kind of interaction with the parent window (except opening/refocusing the child window) without closing the child window first. I have no idea how to do that.
Do anyone has an idea how to do that?
The client is only Firefox (it works in a special kiosk configuration) on Linux.
I read somewhere that I could somehow write an extension but I am basically clueless about extensions and its API.
Edit1:
Example of (simplified) legacy code. Not really sure if all the permissions were required, but this is it: This function opens a window that stays over the parent window and prevents any interaction from the user with the parent window.
function fWindowOpen(url, name) {
netscape.security.PrivilegeManager.enablePrivilege("UniversalBrowserRead");
netscape.security.PrivilegeManager.enablePrivilege("UniversalBrowserWrite");
netscape.security.PrivilegeManager
.enablePrivilege("CapabilityPreferencesAccess");
netscape.security.PrivilegeManager
.enablePrivilege("UniversalPreferencesWrite");
netscape.security.PrivilegeManager
.enablePrivilege("UniversalPreferencesRead");
netscape.security.PrivilegeManager.enablePrivilege("UniversalFileRead");
netscape.security.PrivilegeManager.enablePrivilege("UniversalXPConnect");
window.open(
url,
name,
"screenX=70,dependent=yes,menubar=0,toolbar=0,width=900,height=700,modal=1,dialog=1"
);
}
function fnCapture(){
fWindowOpen("/path/to/document_or_japplet/page","_blank");
}
HTML:
<button value="Capture" property="btnCapture" onclick="javascript:fnCapture();"/>
Edit2: Solution
On a typical extension, on the xul code, define this javascript code:
var dialogExt = {
listener: function(evt) {
// Do work with parameters read through evt.target.getAttribute("attribute_name")
window.openDialog(evt.target.getAttribute("url"), evt.target.getAttribute("name"), evt.target.getAttribute("features"));
}
}
// from examples
document.addEventListener("dialogExtEvent", function(e){ dialogExt.listener(e); }, false, true);
Then, on the web page:
var element = document.createElement("dialogExtElement");
element.setAttribute("url", url);
element.setAttribute("name", name);
element.setAttribute("features", features);
document.documentElement.appendChild(element);
var evt = document.createEvent("Events");
evt.initEvent("dialogExtEvent", true, false);
element.dispatchEvent(evt);
Now, maybe I am missing some security checks to let the code work if it originates from the same host, and how to handle a reference to the document that requested the dialog as means of interaction between the dialog window and it's opener.

The Privilege Manager was deprecated in Firefox 12 and removed in Firefox 17 (briefly restored).
You might want to look into Window.showModalDialog(). However, it is deprecated and is expected to go away within the year, or in 2016 if you go with an extended service release (ESR) of Firefox 38. It may be a temporary solution while you develop an extension.
In order to accomplish the same tasks, you will need to write an extension and ask the user to install it (from Bypassing Security Restrictions and Signing Code, the old information about Privilege Manager):
Sites that require additional permissions should now ask Firefox users to install an extension, which can interact with non-privileged pages if needed.
It is possible to write such an extension using any of the three different extension types:
XUL overlay
Restartless/Bootstrap
Add-on SDK
For the first two types, you would use window.open(). The modal option is in "Features requiring privileges". You will probably also want to look at Window.openDialog().
For the Add-on SDK, you would normally use the open() function in the SDK's window/utils module. Here, again, you will probably want to look at openDialog().
It appears you may be opening content that is supplied from the web in these modal windows. It is unlikely that you will get an extension approved to be hosted on AMO which opens content in such windows which in not included in the add-on release. This does not mean you can not develop the extension and have it installed on your kiosk clients without hosting it on AMO. However, there are additional restrictions in development for Firefox this year which will make this significantly more difficult, see: "Introducing Extension Signing: A Safer Add-on Experience".

You should be able to get similiar window.open behavior, including support for the modal option from the sdk's window/utils module.
You will have to install the onclick listener with a content script, send a message to the addon-main through its port and then open that window from the addon main.

gInitialPages is not defined bootstrapped extensions

I am working on Firefox extension that overwrite new tab page and I need to hide my page URL from address bar. I use this code:
if (gInitialPages.indexOf(NEW_TAB_URL)===-1) gInitialPages.push(NEW_TAB_URL);
It works correctly in XUL Overlay code, but I'm getting an error when I try to make my application restartless and move this code to bootstrap.js:
gInitialPages is not defined
So, how can I use gInitialPages (or anything similar) in bootstrapped extensions?

Bootstrapped/restartless extensions do NOT automagically run in the context of (a) window(s).
bootstrap.js runs in an own context, only once per application instance, not in the browser window.
You'll need to:
Manually enumerate all existing browser windows.
Listen for new browser windows as they are opened.
And then manipulate the variable in those windows.
See Mardak's example on how you could do that, in particular watchWindows and unload.

window.opener is not right

I'm opening a popup and want to have a click action in it cause the execution of some jQuery in the page that opened it. Everything I find online says I should be able to do that with window.opener, (e.g. JQuery - Write to opener window)
But when I console.log window.opener, it's just 'true', not a real object. window.opener.jQuery is undefined as is window.opener.$ and 'window.opener.document'.
Here's the window open code:
window.open('http://google.com' , "moderatorWindow", 'width=300, height=300');
This is in Safari. Other pages are able to launch a popup and when I inspect window.opener on those, I get a real object. What am I doing wrong?

Your variable is true and not an object because of same-domain policy rules. Just like an iframe, if the popup you open is not on the same domain or sub-domain then it is lost to you after you create it. The web would be a very unsecure place if I could say, open a (hidden) iframe on my site to gmail.com and was able to read your email.
Even if the popup is on a sub-domain you have to do extra work and set the document.domain value of both windows to the root domain (eg. mydomain.com). This is to ensure that the popped-up site wants to be known to its parent (again, think security, if my coke.ning.com community could open a hidden iframe to your pepsi.ning.com and do brute force attempts at a login, etc.)
To prove my point try actually going to google.com and opening up Firebug (or Inspector if you're using Safari or Chrome) and doing:
var bob = window.open('http://google.com' , "moderatorWindow", 'width=300, height=300');
bob.window.location.href; // returns "http://www.google.com/"
Lastly, feel free to call jQuery on the child page to modify elements on the same page and vice-versa but you can't use jQuery from one page to modify the dom of the other page. I tried this a few years ago to try to save on some loading time and, unless something has changed, it doesn't work. jQuery seems to be bound to the window object of where it was created. Weird things happen.

Presumably you are calling:
console.log(window.opener);
which should call the toString() method of whatever window.opener references. It should reference a window object, which is a host object. Per the ECMA-262, a host object's toString() method (if it has one) can return anthing it likes, even throw an error (try it on certain IE host objects implemented using ActiveX).
This article might help: http://developer.apple.com/library/safari/#documentation/AppleApplications/Conceptual/SafariJSProgTopics/Articles/Cross-documentmessaging.html