@srcmap/remapping-wasm

@srcmap/remapping-wasm

High-performance source map concatenation and composition powered by Rust via WebAssembly.

Concatenation merges source maps from multiple bundled files into one, adjusting line offsets. Composition chains source maps through multiple transforms (e.g. TS -> JS -> minified) into a single map pointing to original sources. Alternative to @ampproject/remapping.

Install

npm install @srcmap/remapping-wasm

Works in Node.js, browsers, and any WebAssembly-capable runtime. No native compilation required.

Usage

Concatenation

Merge source maps from multiple files into a single combined map:

import { ConcatBuilder } from '@srcmap/remapping-wasm'

const builder = new ConcatBuilder('bundle.js')

// Add source maps with their line offsets in the output
builder.addMap(chunkASourceMapJson, 0)      // chunk A starts at line 0
builder.addMap(chunkBSourceMapJson, 1000)   // chunk B starts at line 1000

const combinedJson = builder.toJSON()

Composition / Remapping

Chain source maps through a transform pipeline into a single map:

import { remap } from '@srcmap/remapping-wasm'

// Your build: original.ts -> intermediate.js -> minified.js
// You have: minified.js.map (outer) and intermediate.js.map (inner)

const composedJson = remap(minifiedSourceMapJson, (source) => {
  // Called for each source in the outer map
  if (source === 'intermediate.js') {
    return intermediateSourceMapJson // upstream source map JSON
  }
  return null // no upstream map, keep as-is
})

API

new ConcatBuilder(file?: string)

Create a builder for concatenating source maps.

Method	Returns	Description
addMap(json, lineOffset)	void	Add a source map JSON at the given line offset
toJSON()	string	Generate the concatenated source map JSON

remap(outerJson, loader)

Compose source maps through a transform chain.

Parameter	Type	Description
outerJson	string	The final-stage source map JSON
loader	(source: string) => string | null	Returns upstream source map JSON, or null

Returns the composed source map as a JSON string.

Build targets

# Node.js (default)
npm run build

# Browser (ES module + .wasm)
npm run build:web

# Bundler (e.g. webpack, vite)
npm run build:bundler

Part of srcmap

High-performance source map tooling written in Rust. See also:

• @srcmap/sourcemap-wasm - Source map parser (WASM)
• @srcmap/generator-wasm - Source map generator (WASM)
• @srcmap/symbolicate-wasm - Stack trace symbolication (WASM)

License

MIT