TypeScript and JavaScript lib generator

This tool is used to generate the web-based lib.dom.d.ts file which is included with TypeScript releases, and as the @types/web package.

Why is my fancy API still not available here?

A feature needs to be supported by more than two major browser engines to be included here, to make sure there is a good consensus among vendors: Gecko (Firefox), Blink (Chrome/Edge), and WebKit (Safari).

If the condition is met but still is not available here, please file an issue.

Build Instructions

To get things setup:

npm install

To generate the .d.ts files

npm run build

To test:

npm run test

To deploy:

npm run migrate

The script will look in for a clone of the TypeScript repo in "../TypeScript", or "./TypeScript" to move the generated files in.

Contribution Guidelines

The dom.generated.d.ts, webworker.generated.d.ts and dom.iterable.generated.d.ts files from the TypeScript repo are used as baselines. For each pull request, we will run the script and compare the generated files with the baseline files. In order to make the tests pass, please update the baseline as well in any pull requests.

It's recommended to first check which spec the wrong type belongs to. Say we are to update IntersectionObserver which belongs to Intersection Observer spec, and then we can do:

1. First check we have the spec name Intersection Observer in inputfiles/idlSources.json. If not, add it.
2. Run npm run fetch-idl "Intersection Observer" && npm run build && npm run baseline-accept.

If the above didn't fix the type issues, we can fix them via json files as a last resort. There are three json files that are typically used to alter the type generation: addedTypes.json, overridingTypes.json, and removedTypes.json. comments.json can used to add comments to the types. Finally, knownTypes.json determine which types are available in a certain environment in case it couldn't be automatically determined.

The format of each file can be inferred from their existing content.

The common steps to send a pull request are:

0. Open or refer to an issue in the TypeScript repo which might get moved back to this repo.
1. Update an IDL or add missing elements to inputfiles/addedTypes.json, overriding elements to inputfiles/overridingTypes.json, or elements to remove to inputfiles/removedTypes.json.
2. Run the build script locally to obtain new dom.generated.d.ts and webworker.generated.d.ts.
3. Update the files in the baselines folder using the newly generated files under generated folder (npm run baseline-accept).

What are the TypeScript team's heuristics for PRs to the DOM APIs

Changes to this repo can have pretty drastic ecosystem effects, because these types are included by default in TypeScript. Due to this, we tend to be quite conservative with our approach to introducing changes. To give you a sense of whether we will accept changes, you can use these heuristics to know up-front if we'll be open to merging.

Fixes

For example, changing a type on a field, or nullability references

• Does the PR show examples of the changes being used in spec examples or reputable websites like MDN?
• Did this change come from an IDL update?
• Does the change appear to be high-impact on a well-used API?
• Would the changes introduce a lot of breaking changes to existing code? For example the large corpus of typed code in DefinitelyTyped.

Additions

For example, adding a new spec or subsection via a new or updated IDL file

• Does the new objects or fields show up in mdn/browser-compat-data? If not, it's likely too soon.
• Is the IDL source from WHATWG?
  • Are the additions available in at least two of Firefox, Safari and Chromium?
• Is the IDL source from W3C?
  • What stage of the W3C process is the proposal for these changes: We aim for Proposed recommendation, but can accept Candidate recommendation for stable looking proposals.
  • If it's at Working draft the additions available in all three of Firefox, Safari and Chromium
• Could any types added at the global scope have naming conflicts?
• Are the new features going to be used by a lot of people?

Removals

For example, removing a browser-specific section of code

• Do the removed objects or fields show up in mdn/browser-compat-data? If so, are they marked as deprecated?
• Does an internet search for the fields show results in blogs/recommendations?
• When was the deprecation (this can be hard to find) but was it at least 2 years ago if so?

Build Instructions

This repo

Code Structure

• src/index.ts: handles the emitting of the .d.ts files.
• src/test.ts: verifies the output by comparing the generated/ and baseline/ contents.

Input Files

• browser.webidl.preprocessed.json: a JSON file generated by Microsoft Edge. Do not edit this file.
  • Due to the different update schedules between Edge and TypeScript, this may not be the most up-to-date version of the spec.
• mdn/apiDescriptions.json: a JSON file generated by fetching API descriptions from MDN. Do not edit this file.
• addedTypes.json: types that should exist in either browser or webworker but are missing from the Edge spec. The format of the file mimics that of browser.webidl.preprocessed.json.
• overridingTypes.json: types that are defined in the spec file but has a better or more up-to-date definitions in the json files.
• removedTypes.json: types that are defined in the spec file but should be removed.
• comments.json: comment strings to be embedded in the generated .js files.
• deprecatedMessage.json: the reason why one type is deprecated. The reason why it is a separate file rather than merge in comment.json is mdn/apiDescriptions.json would also possibly be deprecated.