Switch to ESM

[remcohaszing]

Is your enhancement related to a problem? Please describe.

Currently yaml-language-server is distributed as:

• CommonJS
• UMD
• Faux ESM

These are all outdated practices that aim to provide backwards compatibility for programmatic use. But in reality, they make the project harder to work with.

Describe the solution you would like

• Go ESM only
• Drop CommonJS support
• Drop UMD support
• Drop Node.js 20 support
• Replace Mocha with node:test

Describe alternatives you have considered

• The use of ts-node will likely be problematic. This is why I suggest to use Node.js type-stripping.
• I don’t know how well Mocha works with Node.js type-stripping. This is why I suggest replace Mocha with node:test and drop support for Node.js 20. An alternative would be to build the tests and running its build output.

Additional context

The current state of JavaScript modules is as follows:

• Node.js 12 added support for ESM.
• Node.js 20 added support for require(esm).
• Node.js 22 added support for type-stripping.
• TypeScript 6 is going to remove support for UMD.
• VSCode plans to move to ESM for its client libraries (VSCode client libraries have invalid exports microsoft/vscode#192144 (comment)).
• The upcoming version 3 of the yaml package will be ESM only (Breaking changes for yaml v3 eemeli/yaml#601).
• yaml-language-server is tested against Node.js 20.
• At the moment of writing, Node.js 20 is about to reach EOL.

[datho7561]

Sounds like a good idea. We'd break API, so we'd need to do this as a 2.y.z .