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What is Meros?

Meros is a lightweight utility library that simplifies reading multipart responses in both browser and Node.js environments. At just 642 bytes, it provides a seamless API for consuming multipart/mixed responses through async generators. The name meros comes from Ancient Greek μέρος (méros), meaning “part”.

Quick installation

Install Meros via npm, pnpm, or yarn in seconds

Get started

Start reading multipart responses in minutes

API reference

Explore the complete API documentation

Examples

Learn from real-world usage examples

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Key features

Zero dependencies

No external dependencies means a smaller bundle size and faster installation

Universal support

Works seamlessly in both browser and Node.js environments

High performance

Outperforms alternatives by up to 1.8x in benchmarks

Type safe

Full TypeScript support with generic types for response bodies

Automatic JSON parsing

Automatically detects and parses JSON content-type parts

Framework agnostic

Integrates with any framework - works with Relay, RxJS, and more

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Why Meros?

Multipart responses are commonly used for streaming data, particularly with GraphQL @defer and @stream directives. However, parsing these responses manually can be error-prone and complex. Meros handles all the complexity for you:
  • Automatic boundary detection: Parses the boundary from content-type headers
  • Stream processing: Efficiently processes chunks as they arrive
  • Smart parsing: Automatically parses JSON when detected, falls back to raw strings/buffers
  • Preamble/epilogue handling: Correctly ignores multipart preamble and epilogue sections
  • Multiple modes: Support for both single-part and multi-part yielding strategies
Meros implements the RFC1341 multipart standard, though some advanced features like nested multiparts and alternative/digest/parallel subtypes are not yet supported.

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How it works

Meros takes a response object and returns either:
  • The original response (if it’s not multipart)
  • An async generator that yields parsed parts (if it’s multipart/mixed)
const parts = await fetch('/api').then(meros);

for await (const part of parts) {
  console.log(part.body); // Automatically parsed JSON or raw string
  console.log(part.headers); // Part-specific headers
  console.log(part.json); // true if body is parsed JSON
}
Each part contains:
  • body: The parsed content (JSON object or string/Buffer)
  • headers: Key-value pairs of all headers from that part
  • json: Boolean indicating whether the body was parsed as JSON
Meros is perfect for implementing GraphQL subscriptions with @defer and @stream directives, allowing your application to receive incremental data as it becomes available.

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Use cases

  • GraphQL streaming: Handle @defer and @stream directive responses
  • Progressive data loading: Display data as it arrives rather than waiting for complete responses
  • File uploads: Process multipart form data streams
  • Real-time updates: Stream server-sent data chunks to the client
  • Incremental rendering: Render UI components as their data becomes available

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Next steps

1

Install Meros

Add Meros to your project using your preferred package managerGo to installation →
2

Try the quickstart

Follow our quickstart guide to read your first multipart responseGo to quickstart →
3

Explore the API

Learn about all available options and typesGo to API reference →

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