Suggested solution to #5730 [tsserver] custom command

[mihailik]

See discussion (specifically my comment) in #5730 .

To summarise here, the idea is to allow complex hosts (such as Angular-aware editors) to inject extra commands into tsserver, without recompiling tsserver.js.

Instead of all the complexity of a plugin hosting model, I suggest we turn the table and put the burden of hosting on the actual host interested in running tsserver.

The Angular-editing enrichment will load tsserver.js script content, eval() it, then it has a window to update ts.server.Session.prototype to its liking before the server starts up proper.

[mihailik]

To make it even sweeter, the top-level ts can be exported!

That way no eval() cheats are needed, you simply:

require('tsserver').server.Session.prototype // <-- work your magic

[mhegazy]

closing in favor of #6508 and the associated PRs (#10163, #10160 and #10159)