Convert package to TypeScript automatically

migrate-package-to-typescript.sh

# Create tsconfig.json
echo "{
  \"compilerOptions\": {
    \"declaration\": true,
    \"esModuleInterop\": true,
    \"isolatedModules\": true,
    \"moduleResolution\": \"node\",
    \"outDir\": \"dist\",
    \"strict\": true
  },
  \"include\": [\"src\"],
  \"exclude\": [\"**/*.spec.ts\"]
}" > tsconfig.json

# Replace .babelrc with barebones config
echo "{
  \"presets\": [\"@babel/typescript\", \"@babel/env\"]
}" > .babelrc

# Remove manually created index.d.ts, if any
rm -rf index.d.ts
yarn dlx json -I -f package.json -e "this.files=this.files.filter(x=>x!=='index.d.ts')"

# Rename all js files in src directory to ts
git mv src/index.js src/index.ts
git mv src/index.spec.js src/index.spec.ts

# Modify package.json
npm pkg set 'source'='src/index.ts'
npm pkg set 'types'='src/index.ts'
npm pkg set 'scripts.build-esm'='tsc --outDir dist/esm --module esnext'
npm pkg set 'scripts.build-cjs'='tsc --outDir dist/cjs --module commonjs'
npm pkg set 'scripts.lint'='eslint src --ext .js,.ts'
npm pkg set 'scripts.tsc'='tsc --noEmit'
prev=$(npm pkg get scripts.test)
next=${prev/yarn lint &&/yarn lint && yarn tsc &&}
next=$(echo $next | sed 's/"//g')
npm pkg set 'scripts.test'=$next

# Remove and install dependencies
yarn remove @babel/cli
yarn add @babel/preset-typescript @types/jest @typescript-eslint/parser typescript --dev
yarn dedupe

# Configure ESLint to use @typescript-eslint/parser
yarn dlx json -I -f .eslintrc.json -e "this.parser=\"@typescript-eslint/parser\""

# MANUAL STEPS:
# - Reorder new attributes in package.json manually