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TypeScript

TypeScript

TypeScript is a first-class language on Cloudflare Workers. Cloudflare publishes type definitions to GitHub ↗ and npm ↗ (npm install -D @cloudflare/workers-types). All APIs provided in Workers are fully typed, and type definitions are generated directly from workerd ↗, the open-source Workers runtime.

Generate types that match your Worker’s configuration (experimental)

Cloudflare continuously improves workerd ↗, the open-source Workers runtime. Changes in workerd can introduce JavaScript API changes, thus changing the respective TypeScript types. For example, the urlsearchparams_delete_has_value_arg compatibility flag adds optional arguments to some methods, in order to support new additions to the WHATWG URL standard API.

This means the correct TypeScript types for your Worker depend on:

  1. Your Worker’s Compatibility Date.
  2. Your Worker’s Compatibility Flags.

For example, if you have compatibility_flags = ["nodejs_als"] in your wrangler.toml, then the runtime will allow you to use the AsyncLocalStorage ↗ class in your worker code, but you will not see this reflected in the type definitions in @cloudflare/workers-types.

In order to solve this issue, and to ensure that your type definitions are always up-to-date with your compatibility settings, you can dynamically generate the runtime types (as of wrangler 3.66.0):

Terminal window
npx wrangler types --experimental-include-runtime

This will generate a d.ts file and (by default) save it to .wrangler/types/runtime.d.ts. You will be prompted in the command’s output to add that file to your tsconfig.json’s compilerOptions.types array.

If you would like to commit the file to git, you can provide a custom path. Here, for instance, the runtime.d.ts file will be saved to the root of your project:

Terminal window
npx wrangler types --experimental-include-runtime="./runtime.d.ts"

Note: To ensure that your types are always up-to-date, make sure to run wrangler types --experimental-include-runtime after any changes to your config file.

See the full list of available flags for more details.

Migrating from @cloudflare/workers-types to wrangler types --experimental-include-runtime

The @cloudflare/workers-types package provides runtime types for each distinct compatibility date ↗, which is specified by the user in their tsconfig.json. But this package is superseded by the wrangler types --experimental-include-runtime command.

Here are the steps to switch from @cloudflare/workers-types to using wrangler types with the experimental runtime inclusion:

Uninstall @cloudflare/workers-types
Terminal window
npm uninstall @cloudflare/workers-types
Generate runtime types using wrangler
Terminal window
npx wrangler types --experimental-include-runtime

This will generate a .d.ts file, saved to .wrangler/types/runtime.d.ts by default.

Update your tsconfig.json to include the generated types
{
  "compilerOptions": {
    "types": ["./.wrangler/types/runtime"]
  }
}

Note that if you have specified a custom path for the runtime types file, you should use that in your compilerOptions.types array instead of the default path.

Update your scripts and CI pipelines

When switching to wrangler types --experimental-include-runtime, you’ll want to ensure that your development process always uses the most up-to-date types. The main thing to remember here is that - regardless of your specific framework or build tools - you should run the wrangler types --experimental-include-runtime command before any development tasks that rely on TypeScript. This ensures your editor and build tools always have access to the latest types.

Most projects will have existing build and development scripts scripts, as well as some type-checking. In the example below, we’re adding the wrangler types --experimental-include-runtime before the type-checking script in the project:

{
  "scripts": {
    "dev": "existing-dev-command",
    "build": "-existing-build-command",
    "type-check": "wrangler types --experimental-include-runtime && tsc"
  }
}

In CI, you may have a separate build and test commands. It is best practice to run wrangler types --experimental-include-runtime before other CI commands. For example:

- run: npm run generate-types
- run: npm run build
- run: npm test

By integrating the wrangler types --experimental-include-runtime command into your workflow this way, you ensure that your development environment, builds, and CI processes always use the most accurate and up-to-date types for your Cloudflare Worker, regardless of your specific framework or tooling choices.

Known issues

Transitive loading of @types/node overrides @cloudflare/workers-types

You project’s dependencies may load the @types/node package on their own. As of @types/node@20.8.4 that package now overrides Request, Response and fetch types (possibly others) specified by @cloudflare/workers-types causing type errors.

The way to get around this issue currently is to pin the version of @types/node to 20.8.3 in your package.json like this:

{
  "overrides": {
    "@types/node": "20.8.3"
  }
}

For more information, refer to this GitHub issue ↗.

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