build.mjs

import { promises } from 'node:fs'
import YAML from 'yamljs'
import prettier from 'prettier'
import converter from 'swagger2openapi'
import SwaggerParser from '@apidevtools/swagger-parser'

const swaggerYML = await promises.readFile('yml/swagger.yml', { encoding: 'utf8' }) // 2.0 YML
const openapiJSON = await formatJSON((await converter.convertStr(swaggerYML, {})).openapi)

{ // 3.0 JSON
  await validate(openapiJSON)
  await write('json/openapi.json', openapiJSON)
}

{  // 2.0 JSON
  const swaggerJson = await formatJSON(YAML.parse(swaggerYML))
  await validate(swaggerJson)
  await write('json/swagger.json', swaggerJson)
}

{  // 3.0 YML
  const openapiYML = await prettier.format(YAML.stringify(JSON.parse(openapiJSON)), {
    parser: "yaml"
  })
  await write('yml/openapi.yml', openapiYML)
}

async function formatJSON(jsonStr) {
  return await prettier.format(JSON.stringify(jsonStr), {
    parser: "json"
  });
}

async function write(path, content) {
  return await promises.writeFile(path, content, { encoding: "utf8" });
}

async function validate(json) {
  return await SwaggerParser.validate(JSON.parse(json));
}