Alexandro.Net

Version 1.0.0

@stackline/source-map-js

Generates and consumes source maps

Independent maintenance of source-map-js 1.2.1. Original authors and licenses are retained.

Installation

# Preserve existing imports with an npm alias
npm install source-map-js@npm:@stackline/source-map-js@1.0.0
# Or use the scoped package name in your imports
npm install @stackline/source-map-js@1.0.0

Node.js: >=0.10.0. Read the compatibility and maintenance notes before migrating.

Usage and API

The reference below may retain upstream package names. Use the alias installation above to run those imports with this Stackline release.

Source Map JS

NPM

Difference between original source-map:

TL,DR: it's fork of original source-map@0.6, but with perfomance optimizations.

This journey starts from source-map@0.7.0. Some part of it was rewritten to Rust and WASM and API became async.

It's still a major block for many libraries like PostCSS or Sass for example because they need to migrate the whole API to the async way. This is the reason why 0.6.1 has 2x more downloads than 0.7.3 while it's faster several times.

Downloads count

More important that WASM version has some optimizations in JS code too. This is why community asked to create branch for 0.6 version and port these optimizations but, sadly, the answer was «no». A bit later I discovered the issue created by Ben Rothman (@benthemonkey) with no response at all.

Roman Dvornov (@lahmatiy) wrote a serveral posts (russian, only, sorry) about source-map library in his own Telegram channel. He mentioned the article «Maybe you don't need Rust and WASM to speed up your JS» written by Vyacheslav Egorov (@mraleph). This article contains optimizations and hacks that lead to almost the same performance compare to WASM implementation.

I decided to fork the original source-map and port these optimizations from the article and several others PR from the original source-map.

This is a library to generate and consume the source map format described here.

Use with Node

$ npm install source-map-js

Table of Contents

Examples

Consuming a source map

var rawSourceMap = {
  version: 3,
  file: 'min.js',
  names: ['bar', 'baz', 'n'],
  sources: ['one.js', 'two.js'],
  sourceRoot: 'http://example.com/www/js/',
  mappings: 'CAAC,IAAI,IAAM,SAAUA,GAClB,OAAOC,IAAID;CCDb,IAAI,IAAM,SAAUE,GAClB,OAAOA'
};

var smc = new SourceMapConsumer(rawSourceMap);

console.log(smc.sources);
// [ 'http://example.com/www/js/one.js',
//   'http://example.com/www/js/two.js' ]

console.log(smc.originalPositionFor({
  line: 2,
  column: 28
}));
// { source: 'http://example.com/www/js/two.js',
//   line: 2,
//   column: 10,
//   name: 'n' }

console.log(smc.generatedPositionFor({
  source: 'http://example.com/www/js/two.js',
  line: 2,
  column: 10
}));
// { line: 2, column: 28 }

smc.eachMapping(function (m) {
  // ...
});

Generating a source map

In depth guide: Compiling to JavaScript, and Debugging with Source Maps

With SourceNode (high level API)

function compile(ast) {
  switch (ast.type) {
  case 'BinaryExpression':
    return new SourceNode(
      ast.location.line,
      ast.location.column,
      ast.location.source,
      [compile(ast.left), " + ", compile(ast.right)]
    );
  case 'Literal':
    return new SourceNode(
      ast.location.line,
      ast.location.column,
      ast.location.source,
      String(ast.value)
    );
  // ...
  default:
    throw new Error("Bad AST");
  }
}

var ast = parse("40 + 2", "add.js");
console.log(compile(ast).toStringWithSourceMap({
  file: 'add.js'
}));
// { code: '40 + 2',
//   map: [object SourceMapGenerator] }

With SourceMapGenerator (low level API)

var map = new SourceMapGenerator({
  file: "source-mapped.js"
});

map.addMapping({
  generated: {
    line: 10,
    column: 35
  },
  source: "foo.js",
  original: {
    line: 33,
    column: 2
  },
  name: "christopher"
});

console.log(map.toString());
// '{"version":3,"file":"source-mapped.js","sources":["foo.js"],"names":["christopher"],"mappings":";;;;;;;;;mCAgCEA"}'

API

Get a reference to the module:

// Node.js
var sourceMap = require('source-map');

// Browser builds
var sourceMap = window.sourceMap;

// Inside Firefox
const sourceMap = require("devtools/toolkit/sourcemap/source-map.js");

SourceMapConsumer

A SourceMapConsumer instance represents a parsed source map which we can query for information about the original file positions by giving it a file position in the generated source.

new SourceMapConsumer(rawSourceMap)

The only parameter is the raw source map (either as a string which can be JSON.parse'd, or an object). According to the spec, source maps have the following attributes:

var consumer = new sourceMap.SourceMapConsumer(rawSourceMapJsonData);

SourceMapConsumer.prototype.computeColumnSpans()

Compute the last column for each generated mapping. The last column is inclusive.

// Before:
consumer.allGeneratedPositionsFor({ line: 2, source: "foo.coffee" })
// [ { line: 2,
//     column: 1 },
//   { line: 2,
//     column: 10 },
//   { line: 2,
//     column: 20 } ]

consumer.computeColumnSpans();

// After:
consumer.allGeneratedPositionsFor({ line: 2, source: "foo.coffee" })
// [ { line: 2,
//     column: 1,
//     lastColumn: 9 },
//   { line: 2,
//     column: 10,
//     lastColumn: 19 },
//   { line: 2,
//     column: 20,
//     lastColumn: Infinity } ]

SourceMapConsumer.prototype.originalPositionFor(generatedPosition)

Returns the original source, line, and column information for the generated source's line and column positions provided. The only argument is an object with the following properties:

and an object is returned with the following properties:

consumer.originalPositionFor({ line: 2, column: 10 })
// { source: 'foo.coffee',
//   line: 2,
//   column: 2,
//   name: null }

consumer.originalPositionFor({ line: 99999999999999999, column: 999999999999999 })
// { source: null,
//   line: null,
//   column: null,
//   name: null }

SourceMapConsumer.prototype.generatedPositionFor(originalPosition)

Returns the generated line and column information for the original source, line, and column positions provided. The only argument is an object with the following properties:

and an object is returned with the following properties:

consumer.generatedPositionFor({ source: "example.js", line: 2, column: 10 })
// { line: 1,
//   column: 56 }

SourceMapConsumer.prototype.allGeneratedPositionsFor(originalPosition)

Returns all generated line and column information for the original source, line, and column provided. If no column is provided, returns all mappings corresponding to a either the line we are searching for or the next closest line that has any mappings. Otherwise, returns all mappings corresponding to the given line and either the column we are searching for or the next closest column that has any offsets.

The only argument is an object with the following properties:

and an array of objects is returned, each with the following properties:

consumer.allGeneratedpositionsfor({ line: 2, source: "foo.coffee" })
// [ { line: 2,
//     column: 1 },
//   { line: 2,
//     column: 10 },
//   { line: 2,
//     column: 20 } ]

SourceMapConsumer.prototype.hasContentsOfAllSources()

Return true if we have the embedded source content for every source listed in the source map, false otherwise.

In other words, if this method returns true, then consumer.sourceContentFor(s) will succeed for every source s in consumer.sources.

// ...
if (consumer.hasContentsOfAllSources()) {
  consumerReadyCallback(consumer);
} else {
  fetchSources(consumer, consumerReadyCallback);
}
// ...

SourceMapConsumer.prototype.sourceContentFor(source[, returnNullOnMissing])

Returns the original source content for the source provided. The only argument is the URL of the original source file.

If the source content for the given source is not found, then an error is thrown. Optionally, pass true as the second param to have null returned instead.

consumer.sources
// [ "my-cool-lib.clj" ]

consumer.sourceContentFor("my-cool-lib.clj")
// "..."

consumer.sourceContentFor("this is not in the source map");
// Error: "this is not in the source map" is not in the source map

consumer.sourceContentFor("this is not in the source map", true);
// null

SourceMapConsumer.prototype.eachMapping(callback, context, order)

Iterate over each mapping between an original source/line/column and a generated line/column in this source map.

consumer.eachMapping(function (m) { console.log(m); })
// ...
// { source: 'illmatic.js',
//   generatedLine: 1,
//   generatedColumn: 0,
//   originalLine: 1,
//   originalColumn: 0,
//   name: null }
// { source: 'illmatic.js',
//   generatedLine: 2,
//   generatedColumn: 0,
//   originalLine: 2,
//   originalColumn: 0,
//   name: null }
// ...

SourceMapGenerator

An instance of the SourceMapGenerator represents a source map which is being built incrementally.

new SourceMapGenerator([startOfSourceMap])

You may pass an object with the following properties:

var generator = new sourceMap.SourceMapGenerator({
  file: "my-generated-javascript-file.js",
  sourceRoot: "http://example.com/app/js/"
});

SourceMapGenerator.fromSourceMap(sourceMapConsumer, sourceMapGeneratorOptions)

Creates a new SourceMapGenerator from an existing SourceMapConsumer instance.

var generator = sourceMap.SourceMapGenerator.fromSourceMap(consumer, {
  ignoreInvalidMapping: true,
});

SourceMapGenerator.prototype.addMapping(mapping)

Add a single mapping from original source line and column to the generated source's line and column for this source map being created. The mapping object should have the following properties:

generator.addMapping({
  source: "module-one.scm",
  original: { line: 128, column: 0 },
  generated: { line: 3, column: 456 }
})

SourceMapGenerator.prototype.setSourceContent(sourceFile, sourceContent)

Set the source content for an original source file.

generator.setSourceContent("module-one.scm",
                           fs.readFileSync("path/to/module-one.scm"))

SourceMapGenerator.prototype.applySourceMap(sourceMapConsumer[, sourceFile[, sourceMapPath]])

Applies a SourceMap for a source file to the SourceMap. Each mapping to the supplied source file is rewritten using the supplied SourceMap. Note: The resolution for the resulting mappings is the minimum of this map and the supplied map.

SourceMapGenerator.prototype.toString()

Renders the source map being generated to a string.

generator.toString()
// '{"version":3,"sources":["module-one.scm"],"names":[],"mappings":"...snip...","file":"my-generated-javascript-file.js","sourceRoot":"http://example.com/app/js/"}'

SourceNode

SourceNodes provide a way to abstract over interpolating and/or concatenating snippets of generated JavaScript source code, while maintaining the line and column information associated between those snippets and the original source code. This is useful as the final intermediate representation a compiler might use before outputting the generated JS and source map.

new SourceNode([line, column, source[, chunk[, name]]])

var node = new SourceNode(1, 2, "a.cpp", [
  new SourceNode(3, 4, "b.cpp", "extern int status;\n"),
  new SourceNode(5, 6, "c.cpp", "std::string* make_string(size_t n);\n"),
  new SourceNode(7, 8, "d.cpp", "int main(int argc, char** argv) {}\n"),
]);

SourceNode.fromStringWithSourceMap(code, sourceMapConsumer[, relativePath])

Creates a SourceNode from generated code and a SourceMapConsumer.

var consumer = new SourceMapConsumer(fs.readFileSync("path/to/my-file.js.map", "utf8"));
var node = SourceNode.fromStringWithSourceMap(fs.readFileSync("path/to/my-file.js"),
                                              consumer);

SourceNode.prototype.add(chunk)

Add a chunk of generated JS to this source node.

node.add(" + ");
node.add(otherNode);
node.add([leftHandOperandNode, " + ", rightHandOperandNode]);

SourceNode.prototype.prepend(chunk)

Prepend a chunk of generated JS to this source node.

node.prepend("/** Build Id: f783haef86324gf **/\n\n");

SourceNode.prototype.setSourceContent(sourceFile, sourceContent)

Set the source content for a source file. This will be added to the SourceMap in the sourcesContent field.

node.setSourceContent("module-one.scm",
                      fs.readFileSync("path/to/module-one.scm"))

SourceNode.prototype.walk(fn)

Walk over the tree of JS snippets in this node and its children. The walking function is called once for each snippet of JS and is passed that snippet and the its original associated source's line/column location.

var node = new SourceNode(1, 2, "a.js", [
  new SourceNode(3, 4, "b.js", "uno"),
  "dos",
  [
    "tres",
    new SourceNode(5, 6, "c.js", "quatro")
  ]
]);

node.walk(function (code, loc) { console.log("WALK:", code, loc); })
// WALK: uno { source: 'b.js', line: 3, column: 4, name: null }
// WALK: dos { source: 'a.js', line: 1, column: 2, name: null }
// WALK: tres { source: 'a.js', line: 1, column: 2, name: null }
// WALK: quatro { source: 'c.js', line: 5, column: 6, name: null }

SourceNode.prototype.walkSourceContents(fn)

Walk over the tree of SourceNodes. The walking function is called for each source file content and is passed the filename and source content.

var a = new SourceNode(1, 2, "a.js", "generated from a");
a.setSourceContent("a.js", "original a");
var b = new SourceNode(1, 2, "b.js", "generated from b");
b.setSourceContent("b.js", "original b");
var c = new SourceNode(1, 2, "c.js", "generated from c");
c.setSourceContent("c.js", "original c");

var node = new SourceNode(null, null, null, [a, b, c]);
node.walkSourceContents(function (source, contents) { console.log("WALK:", source, ":", contents); })
// WALK: a.js : original a
// WALK: b.js : original b
// WALK: c.js : original c

SourceNode.prototype.join(sep)

Like Array.prototype.join except for SourceNodes. Inserts the separator between each of this source node's children.

var lhs = new SourceNode(1, 2, "a.rs", "my_copy");
var operand = new SourceNode(3, 4, "a.rs", "=");
var rhs = new SourceNode(5, 6, "a.rs", "orig.clone()");

var node = new SourceNode(null, null, null, [ lhs, operand, rhs ]);
var joinedNode = node.join(" ");

SourceNode.prototype.replaceRight(pattern, replacement)

Call String.prototype.replace on the very right-most source snippet. Useful for trimming white space from the end of a source node, etc.

// Trim trailing white space.
node.replaceRight(/\s*$/, "");

SourceNode.prototype.toString()

Return the string representation of this source node. Walks over the tree and concatenates all the various snippets together to one string.

var node = new SourceNode(1, 2, "a.js", [
  new SourceNode(3, 4, "b.js", "uno"),
  "dos",
  [
    "tres",
    new SourceNode(5, 6, "c.js", "quatro")
  ]
]);

node.toString()
// 'unodostresquatro'

SourceNode.prototype.toStringWithSourceMap([startOfSourceMap])

Returns the string representation of this tree of source nodes, plus a SourceMapGenerator which contains all the mappings between the generated and original sources.

The arguments are the same as those to new SourceMapGenerator.

var node = new SourceNode(1, 2, "a.js", [
  new SourceNode(3, 4, "b.js", "uno"),
  "dos",
  [
    "tres",
    new SourceNode(5, 6, "c.js", "quatro")
  ]
]);

node.toStringWithSourceMap({ file: "my-output-file.js" })
// { code: 'unodostresquatro',
//   map: [object SourceMapGenerator] }

Upstream issues and maintenance review

Upstream origin and triage

Reviewed issues

Primary-source snapshot: 2026-09-29T00:21:42.767424+00:00. Most recently updated 100 open and 30 closed issue/PR entries; PRs removed. This is triage evidence, not a claim of exhaustive review.

Reject invalid indexed-map offsets and mappings outside the generated content before SourceNode line padding (upstream reports 76/77). The regression preserves valid indexed-map text.

The structured snapshot in .stackline/issue-triage.json also records recently closed reports. Issues for unrelated packages in shared monorepositories were qualified as outside this fork’s runtime scope. No maintainer was contacted.

URL parsing, data URL detection, and trailing-slash handling now avoid overlapping regex backtracking, with differential URL fixtures and large-input regressions.

Release changes

Change Log

1.2.1

1.2.0

Allow to pass options to SourceMapGenerator using SourceMapGenerator.fromSourceMap as second argument

var generator = sourceMap.SourceMapGenerator.fromSourceMap(new SourceMapConsumer(), {
  ignoreInvalidMapping: true,
});

1.1.0

Add ignoreInvalidMapping option to SourceMapGenerator. If enabled, source-map-js will not throw an error on the incorrect previous source map. Instead, it will print warnings and ignore broken mappings.

var generator = new sourceMap.SourceMapGenerator({
  file: "my-generated-javascript-file.js",
  sourceRoot: "http://example.com/app/js/",
  ignoreInvalidMapping: true,
});

1.0.3

1.0.2

1.0.1

1.0.0

It doesn't related to this fork:

0.5.6

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0.1.10

Release files and references

Package bytes, npm provenance and the immutable GitHub release were verified for this version. Security checks describe the reviewed release; documented compatibility risks and upstream reports are not blanket claims of resolution.