jstyper

Turns your JavaScript to TypeScript / Flow (adds types, converts requires to imports, etc); ALPHA QUALITY

JsTyper adds {TypeScript, Flow, Closure} types to JavaScript programs using iterative type propagation and the TypeScript Language Services.

Run it

• Interactive online demo
• npm i -g jstyper then jstyper input.js
  • Noteworthy flags:
    • -o <outputDir> (or --outputDir=<outputDir>): where files should be generated
    • --declarations: only generate interface files (*.d.ts)

Features

• Assumes your JS code is correct, and propagates inferred types globally (across different files):
  • From call sites: if you call f(1), it will assume function f can take a number argument. If you call f() somewhere else, it will assume that argument is optional.
  • From function bodies: in function f(x) { return x * 2 } it's obvious x must be a number. Similar constraints appear when you test arguments for nullity or for equality with other values, etc.
  • From call shapes: from x.y() * x.n; it infers x: {y(): void, readonly n: number}
• Rewrites require calls to ES2016 (ES6) imports.
• Rewrites module.exports to ES2016 (ES6) exports.
• Supports writing declarations (*.d.ts) files only with the --declarations flag.
• Writes a summary of imported / required module interfaces in dependencies.d.ts (e.g. if you var foo = require('foo'); foo.bar() it will infer declare module "foo" { export function bar(): void })
• Rewrites var to let

Example

example.js:

function f(x) {
  return x * 2;
}

function g(x, o) {
  if (o.addValue) {
    return f(x) + o.value;
  }
  return o.name == 'default' ? x : 'y';
}

function gg(x, y) {
  var v = g(x, y);
  return v;
}

example.ts:

function f(x: number): number {
  return x * 2;
}

function g(x: number, o: {addValue: boolean, value: any, name: string}) {
  if (o.addValue) {
    return f(x) + o.value;
  }
  return o.name == 'default' ? x : 'y';
}

function gg(x: number, y: {addValue: boolean, value: any, name: string}) {
  let v = g(x, y);
  return v;
}

TODO

• Bundle & support DOM & ES2015+ libs
• Support var foo = require('./bar').foo pattern
• Support var Foo = function() {}; Foo.prototype.bar = ... (create companion interface Foo { bar... })
• Parse and output flow comment / flow types (+ compare with Flow)
• Lint mode
• Split large tests into smaller specs
• Better propagate contextual types in expressions (e.g. in (a && b && c, a ? b : c)
• Use type constraints instead of types to allow local inference passes
• Support merging of symbols added after structural members {x: number} | Foo
• Handle index operators
• Infer x: Promise<T> from (await x): T
• WebDriver test for demo
• Support literal types
• Use const when appropriate in var rewrite.
• Proper cli args parsing + --help
• Better new F() class creation inference

Hack it

• Clone this repo
• Run npm i
• Debug the demo npm start (will auto-reload and auto-run tests after any changes made to the TypeScript sources)
• More options: take a look at package.json's script entries