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Comprehensive JavaScript/ FFI bindings for MoonBit, supporting multiple runtimes and platforms.

v0.10.0 requires MoonBit nightly2025-12-09 or later for ESM#module directive support:

moon 0.1.20251209 (8d6e473 2025-12-09)moonc v0.6.34+7262739a4-nightly (2025-12-09)moonrun 0.1.20251209 (8d6e473 2025-12-09)

If you need stable toolchain compatibility, usev0.8.x.

NPM package bindings have moved: Allmizchi/js/npm/* packages are now in a separate repository:mizchi/npm_typed

$ moon add mizchi/js

Add to yourmoon.pkg.json:

{"import": ["mizchi/js/core","mizchi/js"]}

⚠️ Future Plans: Platform-specific APIs (Node.js, Browser, Deno) will be split into separate packages in the future. The coremizchi/js package will focus on JavaScript built-ins and Web Standard APIs.

Note: Cloudflare Workers bindings have been moved to a separate package:@mizchi/cloudflare-mbt

• MoonBit Cheatsheet - Quick reference for MoonBit syntax
• FFI Best Practice - Best practice for MoonBit JavaScript FFI
• Escape Hatch Pattern - Advanced FFI techniques
• For TypeScript Users - Migration guide from TypeScript

• 🧪Tested: Comprehensive test coverage, production ready
• 🚧Partially: Core functionality implemented, tests incomplete
• 🤖AI Generated: FFI bindings created, needs testing
• 📅Planned: Scheduled for future implementation
• ❌Not Supported: Technical limitations

Themizchi/js/core package provides the foundation for JavaScript interoperability in MoonBit:

Type System

• Any - Opaque type for JavaScript values
• Nullable[T] - Representsnull | T
• Nullish[T] - Representsnull | undefined | T
• Union2[A,B] ~Union5[A,B,C,D,E] - TypeScript union types (A | B)
• Promise[T] - JavaScript Promise wrapper

FFI Operations (zero-cost conversions)

• identity[A,B](value: A) -> B - Type casting using%identity
• any[T](value: T) -> Any - Convert to Any
• Any::cast[T](self) -> T - Cast from Any
• obj["key"],obj["key"] = value - Property access (or_get(key),_set(key, value))
• Any::_call(method, args),Any::_invoke(args) - Method calls

Object & JSON

• new_object(),new_array() - Create JS objects/arrays
• object_keys(),object_values(),object_assign(),object_has_own()
• json_stringify(),json_parse(),json_stringify_pretty()

Async/Promise Support

• run_async(f) - Execute async functions (MoonBit builtin%async.run)
• suspend(f) - Await promises (MoonBit builtin%async.suspend)
• promisify0 ~promisify3 - Convert callbacks to promises
• Promise utilities:resolve,reject,all,race,any,withResolvers

Error Handling

• JsError - Generic JS error type
• ThrowError - Wrapper for thrown errors
• try_sync(op) - Safe wrapper converting JS exceptions to MoonBit errors
• throwable(f) - Convert JS exceptions to ThrowError
• export_sync(op) - Convert MoonBit errors to JS exceptions
• throw_error(msg) - Throw JS Error

Type Checking

• is_object(),is_array(),is_null(),is_undefined(),is_nullish()

Nullish Utilities

• Nullish::to_option(),Nullable::to_option() - Convert to MoonBit Option
• nullable(opt) - Convert Option to JS nullable
• as_any(opt) - Convert Option[Any] to Any

All JavaScript built-in objects are exported frommizchi/js:

Platform-independent Web Standard APIs (browsers, Node.js, Deno, edge runtimes):

Seemizchi/js/web for detailed Web APIs documentation

Moved to separate repository: NPM package bindings are now maintained atmizchi/npm_typed

• ✅Node.js Core APIs -fs,path,process,child_process, etc.
• ✅Deno Runtime - File system, permissions, testing
• ✅Bun Runtime - Process, hashing, glob, file operations
• ✅DOM APIs - Full browser DOM manipulation
• ✅Web Standard APIs - fetch, URL, Streams, Crypto, WebSocket
• 📦React/NPM Packages - Moved tomizchi/npm_typed
• 📦Cloudflare Workers - Moved tomizchi/cloudflare.mbt

• Provide comprehensive JavaScript FFI bindings for MoonBit
• Platform Coverage
  • ✅ Browser DOM and Web APIs
  • ✅ Node.js/Deno/Bun runtime support
  • ✅ JavaScript built-in objects and Web Standard APIs
• Ecosystem
  • 📦 NPM package bindings:mizchi/npm_typed
  • 📦 Cloudflare Workers:mizchi/cloudflare.mbt

// Create JavaScript objectsletobj=@js.from_entries([  ("name",@js.any("Alice")),  ("age",@js.any(30))])// Get propertyletname=obj["name"]// Set propertyobj["age"]=@js.any(31)// Call methodletresult=obj._call("toString", [])// Type castingletage:Int=obj["age"].cast()

MIT