# TypeScript 5.0 Impacts on Vue & Vite Ecosystem

https://devblogs.microsoft.com/typescript/announcing-typescript-5-0-beta/

## TSConfig array extends

We'll make use of this.

Some possible improvements:

- Separate Vue-specific compiler options and strictness-related compiler options.
- Rethink how to target different runtimes, i.e., browser, node, etc., with minimum configurations. Currently we extends from the base configuration, in the future we can just add a new entry without extending.
- Make some magical improvements to the type-checking performance of a project.
* Need to investigate if `--declaration` slows down build, so that we can decide whether to put `declaration` in the config or the command line

## `--moduleResolution bundler`

- replace the good old `node` option.
- `resolvePackageJsonExports` is default on under `moduleResolution: bundler`, so we need `publint` in all our library projects.
- `--moduleResolution bundler` does not support resolution of `require` calls. In TypeScript files, this means the `import mod = require("foo”)` syntax is forbidden
* Will this affect how we bundle the config files with esbuild?

## `--verbatimModuleSyntax`

- We **have to** migrate to it because the old ones would be dropped after 5.5
- Note: this option implies `isolatesModules` (and may supersede it, per the proposal issue), no big deal for Vite, but might affect `vuejs/core`.
- Caveat: `import { writeFile } from "fs”` not allowed in `--module commonjs` https://github.com/microsoft/TypeScript/issues/51479 Would be a small surprise to many users

## `allowArbitraryExtensions` + `node16/nodenext`

- `app.vue.d.ts` no longer works, need `app.d.vue.ts`, a big headache for SSR users

We also need a versioning strategy for `@vue/tsconfig` because we are going to introduce backwards-incompatible compiler options.

## Timeline:

https://github.com/microsoft/TypeScript/issues/51362

| February 28th | TypeScript 5.0 RC Release |
| ------------- | --------------------------- |
| March 14th | TypeScript 5.0 Final Release 🚀 |

## One more thing On the `esm-bundler` entry of `vue`:

https://arethetypeswrong.github.io/
https://twitter.com/atcb/status/1619881540628127744