mlly

What is mlly?

The mlly npm package is a utility library for working with ES module syntax. It provides functions to analyze and manipulate module specifiers and import/export statements.

What are mlly's main functionalities?

Analyzing import/export statements

This feature allows you to analyze the import and export statements within a given piece of code. It returns an object with details about the imports and exports found.

import { analyzeModule } from 'mlly';
const code = `import { foo } from 'bar';`;
const analysis = analyzeModule(code);

Resolving import/export specifiers

This feature helps in resolving the full path of an import specifier based on the current file's location. It is useful for resolving relative paths.

import { resolveImport } from 'mlly';
const resolved = resolveImport('./foo.js', '/path/to/module.js');

Checking for dynamic imports

This feature checks if a given piece of code contains dynamic imports, which are imports that occur within the execution context rather than statically at the top of the file.

import { hasDynamicImport } from 'mlly';
const code = `const module = import('./module.js');`;
const hasDynamic = hasDynamicImport(code);

Other packages similar to mlly

es-module-lexer

This package provides a lexer for ES module syntax, allowing for the analysis of import/export statements. It is similar to mlly in that it can be used to parse and understand module structures, but it is implemented as a low-level lexer written in WebAssembly for performance.

acorn

Acorn is a JavaScript parser that can be used to analyze and manipulate JavaScript code, including ES modules. While mlly is focused on module syntax, Acorn provides a more general-purpose parsing solution that can handle a wide range of JavaScript features.

rollup

Rollup is a module bundler for JavaScript that includes features for analyzing and bundling ES modules. It is more complex and feature-rich than mlly, offering a complete solution for bundling modules for production use, whereas mlly is more focused on module analysis and manipulation.

README

🤝 mlly

Missing ECMAScript module utils for Node.js

Usage

This package is ESM only. Node.js 12+ is needed to use it and it must be imported instead of required.

Install npm package:

# using yarn
yarn add mlly

# using npm
npm install mlly

Import utils:

import { } from 'mlly'

At a glance

While ESM Modules are evolving in Node.js ecosystem, there are still many required features that are still experimental or missing. This package tries to fill in the gap for them.

• Utils to create compatible CommonJS context
• Resolve Utils
  • Exposed from native Node.js implementation
  • Windows paths normalized
  • Supporting custom extensions and /index resolution
  • Supporting custom conditions
• Module Evaluation
  • Allow evaluating modules using data: imports
  • Automatic import rewrite to resolved path using static analyzes
  • Allow bypass ESM Cache
  • Stack-trace support
  • .json loader
• Multiple composable module utils exposed
• Static import analyzes
  • Super fast Regex based implementation
  • Handle most of edge cases
  • Find all static ESM imports
  • Find all dynamic ESM imports
  • Parse static import statement

CommonJS Context

createCommonJS

This utility creates a compatible CommonJS context that is missing in ECMAScript modules.

import { createCommonJS } from 'mlly'

const { __dirname, __filename, require } = createCommonJS(import.meta.url)

Note: require and require.resolve implementation are lazy functions. createRequire will be called on first usage.

Resolving Modules

resolve

Resolve a module by respecting ECMAScript Resolver algorithm (internally using wooorm/import-meta-resolve that exposes Node.js implementation).

Additionally supports resolving without extension and /index similar to CommonJS.

import { resolve } from 'mlly'

// file:///home/user/project/module.mjs
console.log(await resolve('./module.mjs', { url: import.meta.url }))

Resolve options:

• from: URL or string (default is pwd())
• conditions: Array of conditions used for resolution algorithm (default is ['node', 'import'])
• extensions: Array of additional extensions to check if import failed (default is ['.mjs', '.cjs', '.js', '.json'])

resolvePath

Similar to resolve but returns a path instead of URL using fileURLToPath.

import { resolvePath } from 'mlly'

// //home/user/project/module.mjs
console.log(await resolvePath('./module.mjs', { url: import.meta.url }))

createResolve

Create a resolve function with defaults.

import { createResolve } from 'mlly'

const _resolve = createResolve({ url: import.meta.url })

// file:///home/user/project/module.mjs
console.log(await _resolve('./module.mjs'))

Example: Ponyfill import.meta.resolve:

import { createResolve } from 'mlly'

import.meta.resolve = createResolve({ url: import.meta.url })

resolveImports

Resolve all static and dynamic imports with relative paths to full resolved path.

import { resolveImports } from 'mlly'

// import foo from 'file:///home/user/project/bar.mjs'
console.log(await resolveImports(`import foo from './bar.mjs'`, { url: import.meta.url }))

Evaluating Moduls

evalModule

Transform and evaluates module code using dynamic imports.

import { evalModule } from 'mlly'

await evalModule(`console.log("Hello World!")`)

await evalModule(`
  import { reverse } from './utils.mjs'
  console.log(reverse('!emosewa si sj'))
`, { url: import.meta.url })

Options:

• all resolve options
• url: File URL

loadModule

Dynamically loads a module by evaluating source code.

import { loadModule } from 'mlly'

await loadModule('./hello.mjs', { url: import.meta.url })

Options are same as evalModule.

transformModule

• Resolves all relative imports will be resolved
• All usages of import.meta.url will be replaced with url or from option

import { toDataURL } from 'mlly'
console.log(transformModule(`console.log(import.meta.url)`), { url: 'test.mjs' })

Options are same as evalModule.

Import analyzes

findStaticImports

Find all static ESM imports.

Example:

import { findStaticImports } from 'mlly'

console.log(findStaticImports(`
// Empty line
import foo, { bar /* foo */ } from 'baz'
`))

Outputs:

[
  {
    type: 'static',
    imports: 'foo, { bar /* foo */ } ',
    specifier: 'baz',
    code: "import foo, { bar /* foo */ } from 'baz'",
    start: 15,
    end: 55
  }
]

parseStaticImport

Parse a dynamic ESM import statement previusly matched by findStaticImports.

Example:

import { findStaticImports, parseStaticImport } from 'mlly'

const [match0] = findStaticImports(`import baz, { x, y as z } from 'baz'`)
console.log(parseStaticImport(match0))

Outputs:

{
  type: 'static',
  imports: 'baz, { x, y as z } ',
  specifier: 'baz',
  code: "import baz, { x, y as z } from 'baz'",
  start: 0,
  end: 36,
  defaultImport: 'baz',
  namespacedImport: undefined,
  namedImports: { x: 'x', y: 'z' }
}

findDynamicImports

Find all dynamic ESM imports.

Example:

import { findDynamicImports } from 'mlly'

console.log(findDynamicImports(`
const foo = await import('bar')
`))

Outputs:

[
  {
    type: 'dynamic',
    expression: "'bar'",
    code: "import('bar')",
    start: 19,
    end: 32
  }
]

Other Utils

fileURLToPath

Similar to url.fileURLToPath but also converts windows backslash \ to unix slash / and handles if input is already a path.

import { fileURLToPath } from 'mlly'

// /foo/bar.js
console.log(fileURLToPath('file:///foo/bar.js'))

// C:/path
console.log(fileURLToPath('file:///C:/path/'))

normalizeid

Ensures id has either of node:, data:, http:, https: or file: protocols.

import { ensureProtocol } from 'mlly'

// file:///foo/bar.js
console.log(normalizeid('/foo/bar.js'))

loadURL

Read source contents of a URL. (currently only file protocol supported)

import { resolve, loadURL } from 'mlly'

const url = await resolve('./index.mjs', { url: import.meta.url })
console.log(await loadURL(url))

toDataURL

Convert code to data: URL using base64 encoding.

import { toDataURL } from 'mlly'

console.log(toDataURL(`
  // This is an example
  console.log('Hello world')
`))

interopDefault

Return the default export of a module at the top-level, alongside any other named exports.

// Assuming the shape { default: { foo: 'bar' }, baz: 'qux' }
import myModule from 'my-module'
  
// Returns { foo: 'bar', baz: 'qux' }
console.log(interopDefault(myModule))

License

MIT

Changelog

0.2.6 (2021-10-12)

Bug Fixes

• interopDefault: do not override existing props (#7) (9429606)