How can I use the BroadcastChannel API or something similar in Safari 10+?

Question

Problem:

I need a client-side Javascript solution (jQuery is fine) where an event in one browser window/tab can be broadcast to other windows/tabs on the same domain. For example, if a cart is updated in tab A, tabs B and C get notified so we can update some info on the page, or notify the user that page is stale, or something like that.

What I've tried:

The BroadcastChannel API fits my needs perfectly, but does not work in IE 11 or Safari.

So I tried this polyfill so I could use the BroadcastChannel API everywhere. It worked in IE, but not in Safari (I believe BroadcastChannel remained undefined).

I then tried sysend.js , which uses BroadCastChannel if it's available, otherwise fakes it using localStorage. Their demo page works fine in Safari, but on my site, I found it worked in Safari 9, but not 10-12 (tested using BrowserStack and one real Mac running Safari 12). Debugging their script, it seems the storage event that's supposed to fire when localStorage in a different tab is changed simply doesn't fire. But this is actually only a problem when you have document.domain set, which I do.

I believe this is the same as this old Chrome bug. But whereas Chrome had that issue from 2012-2017, Safari apparently introduced it around 2017?

I haven't found anyone else discussing this bug in Safari, but I can prove this pretty easily. Open two tabs that use the same document.domain value and run these scripts:

Tab A:

$(window).on("storage", function (e) {
    alert('storage was modified');
});

Tab B:

localStorage.setItem("test", "123");

In Safari 9, Tab A will pop the alert. In Safari 10+, it won't.

If I remove the document.domain, it works. Note that we are using document.domain on these pages, but they are actually on the same domain in this case. However document.domain is needed for other scenarios across the site, so I can't remove it.

I also tried looking at store.js. It has an event system, but it only seemed to work within the same tab (in any browser). Unless I'm missing something.

So, is there any BroadcastChannel polyfill or similar library that actually works in Safari 10+ when you have a document.domain set? Or any other way to do this?

Notes:

• I'm aware that BroadcastChannel and the "storage" event for localStorage only fire for tabs other than the current one. That is not my issue, and is actually desirable to me.
• I've also seen posts that make me believe an alternate solution relying on localStorage likely will not work in Private Browsing mode in Safari. EDIT: It appears this was fixed in Safari 11 so it does work, but in my tests it didn't share localStorage with any other tabs, even other Private tabs in the same window. So that's not much help. Ideally, a solution would account for this as well, but at this point I'd be happy with anything that worked in Safari 10+ for me. I did see an example in the store.js project where they said they made it so it would fallback to cookies in that case, so it sounds possible at least.
• I tried to think about other ways to do this with a setInterval that checks the localStorage for updates every few seconds or something. Even in theory that seems really hacky and unreliable (how would you know when all pages have "received" the update so you can clear it out?). And how would you know when to do it this hacky way instead of one of the preferred methods using localStorage? Safari 10+ is going to report that it supports localStorage so you can't really feature detect it, right? It "supports" it, it just doesn't work correctly.

Luciolucita

Answer 1

I found a workaround, but I'll leave this question open because I'd still love to see a better answer.

As a last resort, I ended up toggling between two different ways of performing the messaging, depending on browser.

Basically, if it's Safari I use https://github.com/pubkey/broadcast-channel (you can get the minified vanilla JS version from https://github.com/pubkey/broadcast-channel/blob/master/dist/lib/browser.min.js). This seems to work in all versions even when you have a document.domain set. I think it uses indexDB in this case, which seems like total overkill, but I don't seem to have a choice.

It also works in Safari private windows in newer versions of Safari. I have try catches in place in all my script for older versions of Safari in private mode where it would otherwise throw errors.

If it's not Safari, I use sysend.js which uses BroadcastChannel by default and falls back to localStorage for cases like IE 11.

Luciolucita

Note that github.com/pubkey/broadcast-channel only works if the windows to communicate are top level in Safari, but not if one window is an iframe. As Safari doesnt support native BroadcastChannel, it falls back to localStorage. When localStorage is used in an iframe its bound not to just the context of the current domain, but "double keyed" to that domain + window.top domain. – Cystectomy

github.com/pubkey/broadcast-channel reverts to localStorage when needed, so no need to use an additional library – Frequentation

@NicholasHaley I believe I was trying to use the browser-native BroadcastChannel wherever possible. The way I've done it, between the two plugins, it basically uses native BroadcastChannel first, then falls back to a localStorage-based solution, then falls back to an indexDB-based solution. – Luciolucita

@Luciolucita I have a project where I need to do something similar. The "broadcast-channel" lib is able is most cases to find the fallback (either localStorage or IndexedDB) in case native Broadcast Channel support is not available. If you need even more control (as I did) in your project, the second parameter takes an object where you can specify the type. To be clear, github.com/pubkey/broadcast-channe will use native BroadcastChannel where-ever possible. Might simplify your code. See: github.com/pubkey/… – Frequentation

@NicholasHaley Oh, interesting! I guess I never saw that part of the doc. I saw it said "This behaves similar to the BroadcastChannel API" and assumed it didn't actually use the native API at all. I don't have time to play with it, but this could potentially be the real answer to my original question, then. – Luciolucita

It seems either of the two libraries can be used by itself, github.com/jcubic/sysend.js also including the fallback for Safari and IE11 – Raylenerayless

in case somebody ever wants to receive messages from the native Broadcast Channel API in the broadcast-channel package - make sure to add two properties to the message (type and time) bc.postMessage({'foo': 'bar', 'type': 'message', 'time': new Date().getTime() * 1000}) took me quite a while to find that out. – Fairfax