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# Maintaining types for Node.js While JavaScript is a weakly-typed language, there are some complementary tools like [TypeScript][] and [Flow][], which allow developers to annotate the source code of their JavaScript projects. While many people don't annotate their code, or make use of annotations at all, there are enough who do that the project has agreed it's important to work towards having [suitable types for end-users][]. ## High level approach - maintaining types There are a number of ways that types could be maintained for Node.js ranging from shipping them with the Node.js runtime to having them be externally maintained. The different options were discussed as part of the [next-10][] effort and it was agreed that maintaining them externally is the best approach. Some of the advantages to this approach include: * Node.js maintainers do not need to be familiar with any given type system/technology. * Types can be updated without requiring Node.js releases. The agreement was that the ideal flow would be as follows: * APIs are added/documented in the existing Node.js markdown files. * Automation in the Node.js project creates a machine readable JSON representation of the API from the documentation. * Automation within external type projects consumes the JSON and automatically generates a PR to add the API. ## High level approach - development workflow The number of people using TypeScript with Node.js is significant enough that providing a good developer experience is important. While TypeScript is identified specifically, a secondary goal is that what we provide to improve development experience with TypeScript would apply to other type systems and transpiled languages as well. We have agreed that the approach will **NOT** include bundling TypeScript tools with Node.js but instead improve the developer experience for how those tools are installed/configured to work with Node.js. The high level developer experience we are working towards was captured in the [next-10 TypeScript mini-summit](https://github.com/nodejs/next-10/pull/150) and is as follows: 1. When Node.js is started with an entry point that is not a file type that Node.js recognizes, for example `node script.ts`, an informative error message is printed that directs users to a webpage where they can learn how to configure Node.js to support that file type. * If the file was a TypeScript file, a TypeScript specific message with a reference to a link on Nodejs.org specific on learning how to configure TypeScript will be provided. * For other file types a generic message and shared webpage will be used. 2. Node.js gains support for loading configuration from a file. Most, if not all, of the configuration supported by `NODE_OPTIONS` would be supported in this file (which might be the `package.json` that lives near the entry point file). The webpage with instructions would tell users what configuration to put in this file to get Node.js to support their file type. 3. When Node.js is run with the correct configuration, either in a file or `NODE_OPTIONS` or flags, the unknown file type is executed as expected. Some additional specifics around the current approach include: * Loaders already provide a number of the components needed to satisfy the requirements above. They already provide the Node.js options that are needed to achieve many of the requirements above. * `package.json` as the location for the config is potentially a good choice as Node.js already looks for it as part of startup. * The implementation chosen should allow for different configuration in/for different environments/conditions such as production versus development, or different types of hosted environments such as serverless vs traditional, etc.; Node.js would not make any recommendations or have any expectations as to what the separate configuration blocks should be named or what their purposes should be, just that a configuration file should have the ability to provide different configurations for user-defined conditions. * There is no plan to define a default tsconfig.json for all Node.js users * We don't have consensus on providing an opinionated default but that should be explored after the initial steps are complete. * It will be important that as part of the messaging around this functionality that we avoid confusion that could lead people to ship TypeScript files (e.g. `script.ts`) instead of the processed files (e.g. `script.js`). ## Generation/Consumption of machine readable JSON files When you run `make doc` the canonical markdown files used to document the Node.js APIs in the [doc/api][] directory are converted to both an `.html` file and a `.json` file. As part of the regular build/release process both the `html` and `json` files are published to [nodejs.org][]. The generator that does the conversion is in the [tools/doc][] directory. ## Markdown structure The constraints required on the markdown files in the [doc/api][] directory in order to be able to generate the JSON files are defined in the [documentation-style-guide][]. ## Planned changes (as of Jan 1 2022) While JSON files are already being generated and published, they are not structured well enough for them to be easily consumed by the type projects. Generally external teams need some custom scripts along with manual fixup afterwards. There is an ongoing effort to add additional markdown constraints and then update the flow in order to be able to generate a better JSON output. [Flow]: https://flow.org/ [TypeScript]: https://www.typescriptlang.org/ [doc/api]: https://github.com/nodejs/node/tree/HEAD/doc/api [documentation-style-guide]: https://github.com/nodejs/node/blob/HEAD/doc/README.md#documentation-style-guide [next-10]: https://github.com/nodejs/next-10/blob/HEAD/meetings/summit-nov-2021.md#suitable-types-for-end-users [nodejs.org]: https://nodejs.org/en/docs/ [suitable types for end-users]: https://github.com/nodejs/node/blob/HEAD/doc/contributing/technical-priorities.md#suitable-types-for-end-users [tools/doc]: https://github.com/nodejs/node/tree/HEAD/tools/doc