There is no reason why any web document should not still be readable in Lynx, Mosaic, or even WorldWideWeb.
Web applications are a bit more complicated, but that complication is self-inflicted. We developers choose to to hijack users' devices for work that should be done on the server in the name of providing a better user experience, and we make our work harder in the process.
Supporting old browsers isn't that hard. Build a solid foundation of HTML, HTTP GET, and HTTP POST, even if it means doing full page refreshes. You can always layer your AJAX calls and such on top. It's called "progressive enhancement", remember?
I think you are absolutely right with "self-inflicted" --- it brings to mind the frequent discussions here about Slack and their web-based client using hundreds of MB to gigabytes of memory for what is essentially "IRC with some images". Not too long ago they "stopped supporting" older browsers, which was basically a kick in the face to everyone for whom it was working perfectly fine before.
I remember using "webchats" in the late 90s/early 2000s with IE6 (or could be 5/5.5, not sure) on machines with probably 1/100th the processing power and memory of ones today, and they worked perfectly well; complete with things like animated emoticons (they weren't called "emoji" yet) and GIFs that didn't even lag the system unlike what happens today, and that was on a single-core CPU!
A possibly fun project is to create a Slack clone that works with that resource constraint, and uses their API; they have a WebSocket interface which older browsers are obviously not capable of using, but I believe there's a classic AJAX API too.
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I was trying to buy movie tickets online the other day.I tried Firefox then Firefox without ad blockers, then ie, then edge, then chrome on two different desk top machines.
Then my gf bought them on her phone browser.
Thanks mobile first development. How much money must you be costing your adherents?
One of the arguments the article makes is that it doesn't --- thanks to the backwards-compatible nature of the Web, anything that works on an older browser is likely to continue working on the newer one.
That seems backwards.
It's an obvious fact to anyone who does front end web development.