Add WASM bindings using wasm-bindgen

[jp-knj]

Overview

Provides minimal WebAssembly bindings for markdown-rs, addressing the WASM hanging issues mentioned in #182 while following maintainer preference for WASM-only approach (no NAPI).

Background

This PR takes a different approach from #182

• Prev PR: NAPI + WASM hybrid with platform-specific builds
• This PR: Pure WASM solution, simpler and more maintainable

Key Improvements

• Fixes WASM hanging - Resolves the hanging issue reported in Add npm package using napi-rs #182
• No NAPI complexity - Pure WASM
• ESM-first - Uses .mjs extension for proper Node.js module resolution
• Minimal footprint - Single wasm binary (~500KB) vs multiple platform builds

Implementation

import { toHtml, toHtmlWithOptions } from 'markdown-wasm';

// CommonMark
const html = await toHtml('# Hello World');

// With GFM/MDX
const gfmHtml = await toHtmlWithOptions('~text~', { gfm: true });

Why Pure WASM?

Per maintainer feedback on #182:

• Lower maintenance burden (no per-platform builds)
• Universal compatibility (one binary for all)
• No native toolchain requirements
• Simpler CI/CD pipeline

Testing

• Works on Node.js 16+, Bun 1.1+
• No hanging issues
• Comprehensive test suite included
• Examples for basic and advanced usage

Performance

While NAPI may be faster, WASM provides:

• Consistent performance across platforms
• No native compilation for users
• Adequate speed for most use cases

This approach prioritizes maintainability and reliability over maximum performance, aligning with project goals.

Related to #182

[wooorm]

Thanks for working on this!
Could we do with plain npm?
should it be called markdown-rs-wasm, what about markdown-wasm? Something else?

[jp-knj]

I’m not fully confident in this change.
does it look good to you? Happy to adjust if needed.

[ChristianMurphy]

I haven't had a chance to pull down the code and try it out (traveling presently).
But at an approach/strategy level, I'm a lot more comfortable with a single WASM build, over half a dozen single platform builds with N-API bindings.

[punkpeye]

Is the AST compatible with mdast-util-from-markdown ? If so, it would be really nice to expose that.