detypes

Fork from https://github.com/Dunqing/detype, which is a fork from https://github.com/cyco130/detype. Since the original author has not processed the PR for a long time, a patch version has been released for the time being until original repo is active again.

npm i -g @unovue/detypes

Suppose you have a library that you want to provide usage examples for. detypes can help you generate vanilla JavaScript samples from TypeScript samples automatically and remove the burden of maintaining two separate versions of what is essentially the same code.

It is a command line tool and a library that removes type annotations and other TypeScript specific syntax constructs and outputs vanilla JavaScript without altering the source formatting too much. It supports .ts, .tsx, as well as .vue files.

In other words, it turns this:

import type { ParsedPath } from 'node:path'

let x: string

// This comment should be kept

// This comment should be deleted
// Ditto for this
interface Foo {
  // This should go too
  bar: number
}

// This comment should also be kept
export function bar(foo: Foo): Date {
  return new Date()
}

into this:

let x

// This comment should be kept

// This comment should also be kept
export function bar(foo) {
  return new Date()
}

The output is very close to hand-written JavaScript, especially if you were already using Prettier for formatting.

Doesn't tsc already do that?

There are lots of tools for transpiling TypeScript into plain JavaScript (tsc, babel, swc, esbuild, sucrase etc.) but none of them is perfectly suitable for this specific use case. Most of them don't preserve the formatting at all. sucrase comes close, but it doesn't remove comments attached to TypeScript-only constructs.

detypes uses Babel, a small Babel plugin to remove comments attached to TypeScript-only constructs, and Prettier under the hood. For Vue files, it also uses the tools from the VueDX project.

Magic comments

Sometimes you want the generated JavaScript to be slightly different than the TypeScript original. You can use the magic comments feature to achieve this:

Input:

// @detypes: replace
// These two lines will be removed
console.log('Hello from TypeScript')
// @detypes: with
// // Notice the double comments!
// console.log("Hello from JavaScript");
// @detypes: end

Output:

// Notice the double comments!
console.log('Hello from JavaScript')

If you just want to remove the magic comments, you can use the -m CLI flag or the removeMagicComments function to generate uncluttered TypeScript like this:

// These two lines will be removed
console.log('Hello from TypeScript')

System requirements

detypes requires Node version 14.19.3 or later.

CLI Usage

  detypes [-m | --remove-magic-comments] <INPUT> [OUTPUT]

    INPUT   Input file or directory

    OUTPUT  Output file or directory
      (optional if it can be inferred and it won't overwrite the source file)

    -t, --remove-ts-comments
      Remove @ts-ignore and @ts-expect-error comments

    -m, --remove-magic-comments
      Remove magic comments only, don't perform ts > js transform

  detypes [-v | --version]

    Print version and exit

  detypes [-h | --help]

    Print this help and exit

Node API

// Transform TypeScript code into vanilla JavaScript without affecting the formatting
function transform(
// Source code
  code: string,
// File name for the source
  fileName: string,
// Options to pass to prettier
  prettierOptions?: PrettierOptions | null,
): Promise<string>

// Transform the input file and write the output to another file
function transformFile(
  inputFileName: string,
  outputFileName: string,
): Promise<void>

// Remove magic comments without performing the TS to JS transform
export function removeMagicComments(
// Source code
  code: string,
// File name for the source
  fileName: string,
// Options to pass to prettier
  prettierOptions?: PrettierOptions | null,
): string

// Remove magic comments from the input file and write the output to another file
export function removeMagicCommentsFromFile(
  inputFileName: string,
  outputFileName: string,
): Promise<void>

Change log

0.6

• feature: Option to remove @ts-ignore and @ts-expect-error comments
• fix: Preserve newline runs (especially in template literals!)

0.5

• BREAKING CHANGE: Drop support for Node 12
• chore: Set up CI workflows

0.4

• feature: CLI support for removing magic comments
• chore: Improve documentation

0.3

• feature: Magic comments
• feature: Expose type declarations
• fix: Better empty line handling

0.2

• feature: for Vue single file components

0.1

• Initial release

Credits

Dunqing, Fatih Aygün, under MIT License