babel-extract-named-export

babel-extract-named-export

Extract named exports from ES6 files using Babel.

code example:

const fs = require('fs')
const extract = require('babel-extract-named-export')
const sample = fs.readFileSync('/path/to/file.js')

main()
async function main() {
  const res = await extract(sample)
  console.log(res) // { [...]: { ... } }
}

Optionally, pass a search array option to select keys you want to extract:

  const { meta } = await extract(sample, { search: ['meta'] })

By default, the Babel parser is configured to use @babel/preset-env. Depending on your needs, this might not be enough. Most common needs include parsing jsx and Vue files. Fortunately, the package ships with default configurations for both React and Vue:

  const {
    vue,
    react: defaultReactConfiguration,
  } = require('babel-extract-named-export/babel')

  const { meta } = await extract(sample, defaultReactConfiguration)

This is equivalent to this:

  const reactPreset = require('@babel/preset-react')

  const { meta } = await extract(sample, { presets: [reactPreset], plugin: [] })

This is usually enough, but if you ever need to override more properties or not include @babel/preset-env at all, you can pass a transformProps object like this:

  // see https://babeljs.io/docs/en/babel-core
  const { meta } = await extract(sample, { transformProps: { /* ... */ } })

⚠️ Note that if you use a plugins key in transformProps, you would also prevent the plugin to actually do its thing!

Under the hood, the plugin use ast-to-literal to transform extracted keys to Javascript values. Some complex fields, like functions are not supported and will return undefined. If you want the plugin to fallback to the Babel AST node, pass fallback to the plugin:

  const { myFunc } = await extract(sample, { fallback: true })
  // returns { type: "FunctionExpression", ... }

If you never want the AST nodes to be transformed to JS value, you can disable the use of ast-to-literal:

  const { myFunc } = await extract(sample, { useToJs: false })
  // returns { type: "FunctionExpression", ... }

When would you use this?

In my case, I wanted to build a small API out of some metadata stored along with MDX files. Common cases include: create documentation at build time (think prop-types) or run a function server-side (think getStaticProps).

It's also at the core of pris-types!