Script to recursively convert all imports from a directory to ESM compatible imports with `.js` file extensions, will also replace directory imports with direct `/index.js` imports.

renameImportsForEsmSupport.mjs

// @ts-check

/**
 * This script is used to fix imports in the generated typechain types.
 *
 * The generated typechain types are not compatible with ESM imports.
 * They use directory imports and imports without file extensions.
 *
 * Usage:
 *
 * npx hardhat compile
 * node scripts/renameImportsForEsmSupport.js
 */

import * as fs from 'fs'
import * as path from 'path'
import * as url from 'url'

const __filename = url.fileURLToPath(import.meta.url)
const __dirname = path.dirname(__filename)

const directoryPath = path.join(__dirname, 'typechain-types')

const fixImports = filePath => {
  console.log(`Fixing imports for file: ${filePath}`)

  let data = fs.readFileSync(filePath, 'utf8')
  const allMatches = data.match(/from "(\..*?)(?<!\.js)"/g)
  if (!allMatches) return

  // Try to add `.ts` to the import and check if it is a valid file
  // If it is a valid file, append `.js` to the import
  // else, append `/index.js` to the import
  let result = data
  for (const match of allMatches) {
    const importPath = match.replace(/from ["'](.*?)(?<!\.js)["']/, '$1')
    const tsPath = path.join(path.dirname(filePath), `${importPath}.ts`)
    const jsPath = path.join(path.dirname(filePath), `${importPath}.js`)
    const indexTsPath = path.join(path.dirname(filePath), `${importPath}/index.ts`)
    const indexJsPath = path.join(path.dirname(filePath), `${importPath}/index.js`)
    // console.log(`    Checking: ${tsPath}`)
    // console.log(`    Checking: ${jsPath}`)
    // console.log(`    Checking: ${indexTsPath}`)
    // console.log(`    Checking: ${indexJsPath}`)

    // Set the import path prefix (to make sure we don't have `././something.js`)
    let importPathPrefix = './'
    if (importPath.startsWith('./') || importPath.startsWith('../')) {
      importPathPrefix = ''
    }

    // Fix the import
    if (fs.existsSync(jsPath) || fs.existsSync(tsPath)) {
      result = result.replace(match, `from "${importPathPrefix}${importPath}.js"`)
    } else if (fs.existsSync(indexTsPath) || fs.existsSync(indexJsPath)) {
      result = result.replace(match, `from "${importPathPrefix}${importPath}/index.js"`)
    } else {
      console.log(`Could not find file for import: ${match}`)
    }
  }

  fs.writeFileSync(filePath, result, 'utf8')
}

const traverseDirectories = dirPath => {
  fs.readdirSync(dirPath, { withFileTypes: true }).forEach(dirent => {
    const fullPath = path.join(dirPath, dirent.name)
    if (dirent.isDirectory()) {
      traverseDirectories(fullPath)
    } else if (dirent.isFile() && dirent.name.endsWith('.ts')) {
      fixImports(fullPath)
    }
  })
}

console.log(`Fixing imports to be ESM compatible in: ${directoryPath}`)
traverseDirectories(directoryPath)
// fixImports(directoryPath + '/index.ts')

The script supports parent directory path traversal like from "../xxx" as well.

This works both for double " and single quotes ', but will generate double quotes imports ".