TypeScript 7 is out. It is a native port written in Go that delivers faster type-checking and builds while using less memory. This brings huge benefits, especially to large projects where type-checking in the editor can take several seconds to complete.
However, at the time of writing, upgrading to version 7 is not as simple as updating the version using your favourite package manager. Let’s find out why.
What is TypeScript actually made of?
TypeScript is more than just a superset of JavaScript. It is made up of tools that work together to provide type checking and make writing TypeScript a better experience.
At its core is the compiler, which parses the TypeScript code, understands its types, checks for type errors, and transpiles the code to JavaScript. The tsc CLI provides a way to interact with the compiler from the command line.
TypeScript also has a language service, which powers many of the features we use in our editors, such as autocomplete, real-time error highlighting, go-to-definition, and renaming. Without it, writing TypeScript code in an editor would be a horrible experience. Imagine writing your code and catching errors only when you run the CLI.
What changed in TypeScript 7?
The biggest change in TypeScript 7 is not the language itself but how it is implemented. Until TypeScript 6, the compiler and language service were written in TypeScript. In TypeScript 7, both have been ported to Go.
Moving to Go lets TypeScript take better advantage of modern hardware, including shared-memory multithreading that enables more work to happen in parallel.
This was a port rather than a complete redesign of the type system. The TypeScript team deliberately kept the new compiler structurally similar to the old implementation.
The language service changed more significantly, though. Previous versions of TypeScript used a custom protocol through tsserver to communicate with editors. TypeScript 7 now uses the Language Server Protocol (LSP) and has reworked much of the language service to make better use of parallelism.
So while the TypeScript syntax has barely changed, the machinery underneath it has changed considerably.
So why is upgrading not straightforward?
Why can’t I upgrade yet?
The problem is that not every tool uses TypeScript through the tsc CLI.
Many tools in the JavaScript ecosystem, such as typescript-eslint, interact with TypeScript programmatically. Instead of running tsc, they import TypeScript as a package and use its APIs directly in their tooling.
TypeScript 7 does not yet provide a stable API. A new API is expected in TypeScript 7.1, which will be different from the API provided by previous versions.
This means tools that depend on the old TypeScript API cannot simply switch to TypeScript 7.
So for many projects, upgrading TypeScript is not just a question of whether your code compiles. You also need to consider whether the tools surrounding your code are ready for TypeScript 7.
How to upgrade safely
If you haven’t already, upgrade to TypeScript 6 first. The TypeScript team recommends this because TypeScript 7 turns several TypeScript 6 deprecations into errors.
If none of your tooling depends on the TypeScript 6 API, you can install TypeScript 7 normally with npm install -D typescript. Otherwise, use the following side-by-side setup.
For the tools that still depend on TypeScript 6 API, the TypeScript team published a compatibility package: @typescript/typescript6. This package ships with a tsc6 executable which will not clash with the tsc shipped by TypeScript 7.
Install the package using an alias:
npm install -D typescript@npm:@typescript/typescript6Next, install TypeScript 7 under another alias:
npm install -D @typescript/native@npm:typescriptYour devDependencies should look like this:
{
"devDependencies": {
"@typescript/native": "npm:typescript@^7.0.2",
"typescript": "npm:@typescript/typescript6@^6.0.2"
}
}With this setup, tsc runs TypeScript 7, while tools that import TypeScript directly can continue using the TypeScript 6 API.
This is a temporary workaround while the ecosystem catches up with TypeScript 7’s new architecture.