bare-type-stripper

bare-type-stripper

Heuristic lexer for stripping TypeScript type syntax to produce plain JavaScript. Stripped regions are replaced with spaces so source positions and line numbers are preserved.

Usage

const strip = require('bare-type-stripper')

strip(`
  const x: number = 1
  function f<T>(xs: T[]): T { return xs[0] }
`).toString()

// '
//   const x         = 1
//   function f   (xs   )    { return xs[0] }
// '

API

See the bare-type-stripper reference.

What gets stripped

Construct	Example
Type annotations	const x: number = 1
Type aliases	type Foo = number
Interfaces	interface Foo { x: number }
Type-only imports/exports	import type { Foo } from 'mod'
Generics at declarations	function f<T>(x: T): T
Generics at call sites	foo<number>()
Generic arrow functions	<T>(x: T) => x
Type assertions	x as Foo, x satisfies Foo
Non-null assertion	obj!.foo
Optional parameter marker	function f(x?: T)
Definite assignment	let x!: number
Class member modifiers	public, private, readonly, etc.
implements clauses	class C implements I
declare statements	declare const x: number
Overload signatures	function f(x: string): void
Abstract members	abstract foo(): void

What is left alone

• Decorators - they emit runtime code and are valid JavaScript syntax.

What throws

Constructs with runtime semantics that a purely lexical stripper cannot reproduce are marked with the ERROR flag, and strip() throws a SyntaxError when it meets one:

• enum / const enum declarations - they emit a runtime object.
• namespace / module declarations with bodies - they emit runtime code.
• Parameter properties - constructor(public x: number) implies a this.x = x assignment that stripping the modifier would silently lose.
• Old-style angle-bracket type assertions (<Foo>expr) - indistinguishable from JSX, which is not supported.

Limitations

The stripper targets plain .ts sources; JSX (.tsx) is not supported and is reported as non-erasable syntax.

Threat model

bare-type-stripper is one of the addons Bare compiles into its binary, so it inherits Bare's threat model. See docs/threat-model.md for where this addon sits in it.

License

Apache-2.0