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It's surprisingly robust and non-lossy as it stands right now, in big part thanks to how similar flow and typescript definition files are. Please see the output inthis flow-typed PR for the state of the output.

Install usingnpm i flowgen --save

import{compiler}from'flowgen';// To compile a d.ts fileconstflowdef=compiler.compileDefinitionFile(filename);// To compile a stringconstflowdef=compiler.compileDefinitionString(str);// To compile a typescript test file to JavaScript// esTarget = ES5/ES6 etcconsttestCase=compiler.compileTest(path,esTarget)

Recommended second step:

import{beautify}from'flowgen';// Make the definition human readableconstreadableDef=beautify(generatedFlowdef);

Standard usage (will produceexport.flow.js):

npm i -g flowgenflowgen lodash.d.ts

-o / --output-file [outputFile]: Specifies the filename of the exported file, defaults to export.flow.js

--flow-typed-format: Format output so it fits in the flow-typed repo--compile-tests: Compile any sibling <filename>-tests.ts files found--no-inexact: Do not mark object types as inexact (using `...`)--no-module-exports: Convert `export = Type` only to default export, instead of `declare module.exports: Type`--interface-records: Convert TypeScript interfaces to Exact Objects--no-jsdoc: Ignore TypeScript JSDoc--add-flow-header: Add `// @flow` to generated files. Should be used for libs.

Namespaces have been a big headache. What it does right now is that it splits any namespace out into prefixed global scope declarations instead. It works OK, but its not pretty and there's some drawbacks to it.

Definitions in TS and flow are often quite different, and imported types from other libraries don't usually havea one-to-one mapping. Common cases areReact.ReactElement,React.CSSPropsetc.This might require manual processing, or we add a set of hardcoded mutations that handle common cases.

Lodash has been one of the reference libraries i've worked with when creating theconverter. The definition is mostly just a series of interfaces with the same name being re-declared over and over again for each function, which doesn't translate to flow at all. There's multiple ways of solving this but I don't have a great solution for it in place yet.

If your typescript definition files are built inlib add below shell script and run it.

foriin$(find lib -type f -name"*.d.ts");do sh -c"flowgen$i -o${i%.*.*}.js.flow";done;

So if you have definition files in different dir, you can renamelib and run the script.

Here’s an example of the above as an npm script inpackage.json that excludes any typescript definition files found insidenode_modules:

"scripts": {"build:flowtypes":"find . -type f -not -path './node_modules/*' -name '*.d.ts' -exec sh -c 'yarn flowgen --add-flow-header $1 -o ${1%.*.*}.js.flow' _ '{}'\\;"  }

You can then have abuild script that generates flow types along the lines oftsc --build && npm run build:flowtypes.

All help is appreciated. Pleasetweet at me if you want some help getting started, or just want to discuss ideas on how to solve the trickier parts.

• git pull origin master
• yarn compile
• Change the version inpackage.json
• git add .
• `git commit -m "New release"
• npm publish
• git push