How can I load a shared web worker with a user-script?
Precondition
- As you've researched and as it has been mentioned in comments,
SharedWorker
's URL is subject to the Same Origin Policy. - According to this question there's no CORS support for
Worker
's URL. - According to this issue
GM_worker
support is now a WONT_FIX, and seems close enough to impossible to implement due to changes in Firefox. There's also a note that sandboxedWorker
(as opposed tounsafeWindow.Worker
) doesn't work either.
Design
What I suppose you want to achieve is a @include *
userscript that will collect some statistics or create some global UI what will appear everywhere. And thus you want to have a worker to maintain some state or statistic aggregates in runtime (which will be easy to access from every instance of user-script), and/or you want to do some computation-heavy routine (because otherwise it will slow target sites down).
In the way of any solution
The solution I want to propose is to replace SharedWorker
design with an alternative.
- If you want just to maintain a state in the shared worker, just use Greasemonkey storage (
GM_setValue
and friends). It's shared among all userscript instances (SQLite behide the scenes). - If you want to do something computation-heavy task, to it in
unsafeWindow.Worker
and put result back in Greasemonkey storage. - If you want to do some background computation and it must be run only by single instance, there are number of "inter-window" synchronisation libraries (mostly they use
localStorage
but Greasemomkey's has the same API, so it shouldn't be hard to write an adapter to it). Thus you can acquire a lock in one userscript instance and run your routines in it. Like, IWC or ByTheWay (likely used here on Stack Exchange; post about it).
Other way
I'm not sure but there may be some ingenious response spoofing, made from ServiceWorker
to make SharedWorker
work as you would like to. Starting point is in this answer's edit.
I am pretty sure you want a different answer, but sadly this is what it boils down to.
Browsers implement same-origin-policies to protect internet users, and although your intentions are clean, no legit browser allows you to change the origin of a sharedWorker.
All browsing contexts in a sharedWorker
must share the exact same origin
- host
- protocol
- port
You cannot hack around this issue, I've trying using iframes in addition to your methods, but non will work.
Maybe you can put it your javascript file on github and use their raw.
service to get the file, this way you can have it running without much efforts.
Update
I was reading chrome updates and I remembered you asking about this. Cross-origin service workers arrived on chrome!
To do this, add the following to the install event for the SW:
self.addEventListener('install', event => {
event.registerForeignFetch({
scopes: [self.registration.scope], // or some sub-scope
origins: ['*'] // or ['https://example.com']
});
});
Some other considerations are needed aswell, check it out:
Full link: https://developers.google.com/web/updates/2016/09/foreign-fetch?hl=en?utm_campaign=devshow_series_crossoriginserviceworkers_092316&utm_source=gdev&utm_medium=yt-desc
You can use fetch()
, response.blob()
to create an Blob URL
of type application/javascript
from returned Blob
; set SharedWorker()
parameter to Blob URL
created by URL.createObjectURL()
; utilize window.open()
, load
event of newly opened window
to define same SharedWorker
previously defined at original window
, attach message
event to original SharedWorker
at newly opened window
s.
javascript
was tried at console
at How to clear the contents of an iFrame from another iFrame, where current Question URL should be loaded at new tab
with message
from opening window
through worker.port.postMessage()
event handler logged at console
.
Opening window
should also log message
event when posted from newly opened window
using worker.postMessage(/* message */)
, similarly at opening window
window.worker = void 0, window.so = void 0;
fetch("https://cdn.rawgit.com/viziionary/Nacho-Bot/master/webworker.js")
.then(response => response.blob())
.then(script => {
console.log(script);
var url = URL.createObjectURL(script);
window.worker = new SharedWorker(url);
console.log(worker);
worker.port.addEventListener("message", (e) => console.log(e.data));
worker.port.start();
window.so = window.open("https://stackoverflow.com/questions/"
+ "38810002/"
+ "how-can-i-load-a-shared-web-worker-"
+ "with-a-user-script", "_blank");
so.addEventListener("load", () => {
so.worker = worker;
so.console.log(so.worker);
so.worker.port.addEventListener("message", (e) => so.console.log(e.data));
so.worker.port.start();
so.worker.port.postMessage("hi from " + so.location.href);
});
so.addEventListener("load", () => {
worker.port.postMessage("hello from " + location.href)
})
});
At console
at either tab
you can then use, e.g.; at How to clear the contents of an iFrame from another iFrame worker.postMessage("hello, again")
at new window
of current URL How can I load a shared web worker with a user-script?, worker.port.postMessage("hi, again");
where message
events attached at each window
, communication between the two window
s can be achieved using original SharedWorker
created at initial URL.