unbundle/unbundle.js

import/export & node_modules in the browser, without the bundling

const { readFileSync } = require('fs')
const { dirname, relative, resolve } = require('path')
const { parse, visit, types, print } = require('recast')
const { sync: resolveJS } = require('resolve')
const babelParser = require('recast/parsers/babel')
const sourcemapRegex = /\/\/[#@] sourceMappingURL=(?!\w+:)([^\s]+)$/
module.exports = (entry, { recurse = true, root = '/', verbose = false } = {}) => {
  return process(resolve(entry), new Map())
  function relocate (importPath, source) {
    const dependency = resolveJS(importPath, {
      extensions: ['.mjs', '.js'],
      basedir: dirname(source),
      packageFilter: (pkg) => ({
        main: pkg.module || pkg['jsnext:main'] || pkg.main
      })
    })
    const relocated = /^(\.|\/|https?:\/\/)/.test(importPath)
      ? './' + relative(dirname(source), dependency) // File or HTTP
      : root + dependency.substr(dependency.indexOf('node_modules')) // NPM
    return { dependency, relocated }
  }
  function process (source, processed) {
    if (verbose) console.log(`Processing: ${relative('', source)}`)
    if (processed.has(source)) return processed
    else processed.set(source)
    const to = source.includes('node_modules')
      ? source.substr(source.indexOf('node_modules'))
      : relative(dirname(entry), source)
    const raw = readFileSync(source)
    const map = sourcemapRegex.test(raw) && decodeURI(RegExp.$1)
    if (verbose && map) console.log(`Source map: ${map}`)
    const ast = parse(raw, { parser: babelParser })
    visit(ast, {
      visitImport (path) { visitor.call(this, path, path.parent.node.arguments, 0) },
      visitImportDeclaration: visitor,
      visitExportNamedDeclaration: visitor,
      visitExportAllDeclaration: visitor
    })
    function visitor (path, parent = path.node, node = 'source') {
      if (parent[node] && parent[node].type === 'StringLiteral') {
        const { dependency, relocated } = relocate(parent[node].value, source)
        parent[node] = types.builders.literal(relocated)
        if (recurse) process(dependency, processed)
      }
      this.traverse(path)
    }
    const { code } = print(ast, { quote: 'single' })
    return processed.set(source, { code, map, to, from: source })
  }
}