Generating an Import Map

genImportMap.js

import fs from 'node:fs'

const imports = [
    { alias: 'firebase/app',      path: '@firebase/app' },
    { alias: 'firebase/auth',     path: '@firebase/auth' },
    { alias: 'firebase/database', path: '@firebase/database' }
]

if (!fs.existsSync('node_modules')) {
    console.error('Please run `npm i`')
    process.exit(1)
}

const pkgJson = path => JSON.parse(fs.readFileSync(`${path}/package.json`).toString())
const getMainPath = pkg => pkg.browser || pkg.module || undefined
function getEntryPoint(pkg, path) {
    const mainPath = getMainPath(pkg)
    if (mainPath === undefined) return undefined

    const entryPoint = `./node_modules/${path}/${mainPath}`
    if (!fs.existsSync(entryPoint)) {
        console.error(`${entryPoint} is not a real file`)
        process.exit(1)
    }

    return entryPoint
}

const importMap = {
    imports: {},
    // scopes:  {}
}
const deps = new Set()

for (const {alias, path} of imports) {
    const pkg = pkgJson(`node_modules/${path}`)

    Object.keys(pkg.dependencies).forEach(dep => deps.add(dep))
    // deps.add(path)

    const entryPoint = getEntryPoint(pkg, path)
    importMap.imports[alias] = entryPoint
    importMap.imports[path]  = entryPoint
}

for (const dep of deps) {
    const pkg = pkgJson(`node_modules/${dep}`)

    const entryPoint = getEntryPoint(pkg, dep)
    importMap.imports[dep] = entryPoint
}

const indent = '    '

const stringified = JSON.stringify(importMap, undefined, 4)
    .split('\n')
    .map(line => `${indent}${indent}${line}`)
    .join('\n')

const importmapTag = /<script type="importmap">[\s\S]*?<\/script>/

const indexHtml = fs.readFileSync('index.html').toString()
const modified = indexHtml.replace(importmapTag, `<script type="importmap">\n${stringified}\n${indent}</script>`)
fs.writeFileSync('index.html', modified)