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TypeScript

TypeScript is a first-class language on Cloudflare Workers. All APIs provided in Workers are fully typed, and type definitions are generated directly from workerd ↗, the open-source Workers runtime.

We recommend you generate types for your Worker by running wrangler types. Cloudflare also publishes type definitions to GitHub ↗ and npm ↗ (npm install -D @cloudflare/workers-types).

Generate types that match your Worker's configuration

Cloudflare continuously improves workerd ↗, the open-source Workers runtime. Changes in workerd can introduce JavaScript API changes, thus changing the respective TypeScript types.

This means the correct types for your Worker depend on:

  1. Your Worker's compatibility date.
  2. Your Worker's compatibility flags.
  3. Your Worker's bindings, which are accessed on the env object.
  4. Any module rules you have specified in your Wrangler configuration file under rules.

For example, the runtime will onlly allow you to use the AsyncLocalStorage ↗ class if you have compatibility_flags = ["nodejs_als"] in your Wrangler configuration file. This should be reflected in the type definitions.

To ensure that your type definitions always match your Worker's configuration, you can dynamically generate types by running:

Terminal window
npx wrangler types

See the wrangler types command docs for more details.

This will generate a d.ts file and (by default) save it to worker-configuration.d.ts. This will include Env types based on your Worker bindings and runtime types based on your Worker's compatibility date and flags.

You should then add that file to your tsconfig.json's compilerOptions.types array. If you have the nodejs_compat compatibility flag, you should also install @types/node.

You can commit your types file to git if you wish.

Migrating from @cloudflare/workers-types to wrangler types

We recommend you use wrangler types to generate runtime types, rather than using the @cloudflare/workers-types package, as it provides better support for combinations of compatibility date ↗ and compatibility flags. Note that there are no plans to stop publishing the @cloudflare/workers-types package.

1. Uninstall @cloudflare/workers-types

Terminal window
npm uninstall @cloudflare/workers-types

2. Generate runtime types using Wrangler

Terminal window
npx wrangler types

This will generate a .d.ts file, saved to worker-configuration.d.ts by default. This will also generate Env types. If for some reason you do not want to include those, you can set --include-env=false.

You can now remove any imports from @cloudflare/workers-types in your Worker code.

3. Make sure your tsconfig.json includes the generated types

{
  "compilerOptions": {
    "types": ["worker-configuration.d.ts"]
  }
}

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.

4. Add @types/node if you are using nodejs_compat (Optional)

If you are using the nodejs_compat compatibility flag, you should also install @types/node.

Terminal window
npm i @types/node

Then add this to your tsconfig.json.

{
  "compilerOptions": {
    "types": ["worker-configuration.d.ts", "node"]
  }
}

5. Update your scripts and CI pipelines

Regardless of your specific framework or build tools, you should run the wrangler types command before any tasks that rely on TypeScript.

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

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

We recommend you commit your generated types file for use in CI. Alternatively, you can run wrangler types before other CI commands, as it should not take more than a few seconds. For example:

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

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 ↗.

Resources

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