Announcement: Version 4 is the next release of xterm.js

[Tyriar]

Just a heads up to those watching the repo that 3.14 will be the last 3.x release before moving to v4. In v4 we will be officially dropping IE11 support (#1889), removing some deprecated APIs (#2029, #1371, #2142), and adding/stabilizing a bunch of new ones (#2076, #2075), as well as cleaning up how builds are don't which will result in importing lib/xterm.js instead of build/xterm.js (#1314).

While the big theme of v3 was the shiny new renderer and a well defined API via TypeScript typings, the theme of v4 is going to be cleaning up some of the mess that's accumulated over the past few years and enabling consumers of xterm.js to do more via the new addon, buffer and selection APIs that are coming in v3.14 (#2065).

If you're a user and want to upgrade to 4 when it comes out, please make sure you review the events that are being removed and speak up if you are impacted by this #2008 (comment), that and removing support for old addons are the planned major breakages. Also any feedback on how new addons work would be appreciated before it's too late (Examples: 1, 2, 3). Note that the zmodem and terminado addons we will not provide alternatives for, instead relying on the greater community/domain experts to develop equivalent addons.

See the list of planned changes here: https://github.com/xtermjs/xterm.js/issues?q=is%3Aopen+is%3Aissue+milestone%3A4.0.0

Looking back, it apparently took v3 a total of 5 months to release after 2.9.2 😱! I definitely don't want a repeat of that but it could take a bit longer than the typical 1 month iteration we normally do. Because of the relatively small list of things we want to deliver it should be much easier to not see this push out too much.

[Tyriar]

Closing/unpinning in prep of release