Design Meeting Notes, 1/10/2025

DRANK

Make lib Replacement Opt-In by Default https://github.com/microsoft/TypeScript/pull/60829 Since TypeScript 4.5, we've supported loading lib files from node_modules if something is located in @typescript/lib-*. But this lib replacement is on for everyone by default, and that leads to us doing a whole bunch of module resolution all the time at project load going up the spine add file watchers for each of the directories that don't exist. This is a perf hit for everyone (and it's noisy to look at when diagnosing issues) so we want to make it opt-in. According to a rudimentary search, 352 files across all of GitHub use a custom dom. Limited impact? 2 major groups who originally asked for this? People who need to lock on an older dom file like @types/web. People who want a custom version of the built-in lib. How do we roll this out? Introduce this in 5.8, and then make it the default in 6.0.