source-map

What is source-map?

The source-map npm package provides utilities for generating and consuming source maps, which are files that map from the transformed source to the original source, enabling the browser to reconstruct the original source and present it in the developer tools. Source maps are commonly used to debug minified code or transpiled code (e.g., from TypeScript or Babel) in an easier-to-read format.

What are source-map's main functionalities?

Generating a source map

This feature allows you to create a source map that maps the code from a minified file back to its original source files. The code sample represents a simple source map in JSON format.

{"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,MAAM"}

Consuming a source map

This feature allows you to consume a source map and extract information from it, such as the original source files. The code sample demonstrates how to use SourceMapConsumer to read a source map.

const sourceMap = require('source-map');
const consumer = await new sourceMap.SourceMapConsumer('{"version":3,"sources":["foo.js"],"names":["bar"],"mappings":"AAAA","file":"foo.min.js"}');
console.log(consumer.sources); // ['foo.js']

Finding the original position for a generated position

This feature allows you to find the original source position corresponding to a line and column in the generated source. The code sample shows how to retrieve the original position using SourceMapConsumer.

const sourceMap = require('source-map');
const consumer = await new sourceMap.SourceMapConsumer('{"version":3,"sources":["foo.js"],"names":["bar"],"mappings":"AAAA","file":"foo.min.js"}');
const originalPosition = consumer.originalPositionFor({ line: 1, column: 10 });
console.log(originalPosition); // { source: 'foo.js', line: 1, column: 10, name: 'bar' }

Mapping the original source back to the generated code

This feature allows you to map positions in the original source to the corresponding positions in the generated code. The code sample demonstrates how to add a mapping to a SourceMapGenerator instance.

const sourceMap = require('source-map');
const generator = new sourceMap.SourceMapGenerator({ file: 'foo.min.js' });
generator.addMapping({
  generated: { line: 1, column: 10 },
  original: { line: 1, column: 10 },
  source: 'foo.js'
});
const map = generator.toString();
console.log(map);

Other packages similar to source-map

source-map-support

This package provides source map support for stack traces in node.js. It uses source maps to map error stack traces from generated code back to the original sources. It is similar to source-map but focuses more on integrating source map support into node.js environments.

sourcemap-codec

sourcemap-codec is a library for encoding and decoding the mappings field of source maps. It is a lower-level utility compared to source-map and is used when you need to work directly with the mappings field, which is a VLQ-encoded string.

README

Source Map

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

This library is written in the Asynchronous Module Definition format, and works in the following environments:

• Modern Browsers supporting ECMAScript 5 (either after the build, or with an AMD loader such as RequireJS)

• Inside Firefox (as a JSM file, after the build)

• With NodeJS versions 0.8.X and higher

Node

$ npm install source-map

Building from Source (for everywhere else)

Install Node and then run

$ git clone https://[e-mail]/mozilla/source-map.git
$ cd source-map
$ npm link .

Next, run

$ node Makefile.dryice.js

This should spew a bunch of stuff to stdout, and create the following files:

• dist/source-map.js - The unminified browser version.

• dist/source-map.min.js - The minified browser version.

• dist/SourceMap.jsm - The JavaScript Module for inclusion in Firefox source.

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:

// NodeJS
var sourceMap = require('source-map');

// Browser builds
var sourceMap = window.sourceMap;

// Inside Firefox
let sourceMap = {};
Components.utils.import('resource:///modules/devtools/SourceMap.jsm', sourceMap);

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:

• version: Which version of the source map spec this map is following.

• sources: An array of URLs to the original source files.

• names: An array of identifiers which can be referrenced by individual mappings.

• sourceRoot: Optional. The URL root from which all sources are relative.

• sourcesContent: Optional. An array of contents of the original source files.

• mappings: A string of base64 VLQs which contain the actual mappings.

• file: Optional. The generated filename this source map is associated with.

SourceMapConsumer.prototype.computeColumnSpans()

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

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:

• line: The line number in the generated source.

• column: The column number in the generated source.

and an object is returned with the following properties:

• source: The original source file, or null if this information is not available.

• line: The line number in the original source, or null if this information is not available.

• column: The column number in the original source, or null or null if this information is not available.

• name: The original identifier, or null if this information is not available.

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:

• source: The filename of the original source.

• line: The line number in the original source.

• column: The column number in the original source.

and an object is returned with the following properties:

• line: The line number in the generated source, or null.

• column: The column number in the generated source, or null.

SourceMapConsumer.prototype.allGeneratedPositionsFor(originalPosition)

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

• source: The filename of the original source.

• line: The line number in the original source.

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

• line: The line number in the generated source, or null.

• column: The column number in the generated source, or null.

SourceMapConsumer.prototype.sourceContentFor(source)

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

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.

• callback: The function that is called with each mapping. Mappings have the form { source, generatedLine, generatedColumn, originalLine, originalColumn, name }

• context: Optional. If specified, this object will be the value of this every time that callback is called.

• order: Either SourceMapConsumer.GENERATED_ORDER or SourceMapConsumer.ORIGINAL_ORDER. Specifies whether you want to iterate over the mappings sorted by the generated file's line/column order or the original's source/line/column order, respectively. Defaults to SourceMapConsumer.GENERATED_ORDER.

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:

• file: The filename of the generated source that this source map is associated with.

• sourceRoot: A root for all relative URLs in this source map.

• skipValidation: Optional. When true, disables validation of mappings as they are added. This can improve performance but should be used with discretion, as a last resort. Even then, one should avoid using this flag when running tests, if possible.

SourceMapGenerator.fromSourceMap(sourceMapConsumer)

Creates a new SourceMapGenerator based on a SourceMapConsumer

• sourceMapConsumer The SourceMap.

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:

• generated: An object with the generated line and column positions.

• original: An object with the original line and column positions.

• source: The original source file (relative to the sourceRoot).

• name: An optional original token name for this mapping.

SourceMapGenerator.prototype.setSourceContent(sourceFile, sourceContent)

Set the source content for an original source file.

• sourceFile the URL of the original source file.

• sourceContent the content of the source file.

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 minimium of this map and the supplied map.

• sourceMapConsumer: The SourceMap to be applied.

• sourceFile: Optional. The filename of the source file. If omitted, sourceMapConsumer.file will be used, if it exists. Otherwise an error will be thrown.

• sourceMapPath: Optional. The dirname of the path to the SourceMap to be applied. If relative, it is relative to the SourceMap.

  This parameter is needed when the two SourceMaps aren't in the same directory, and the SourceMap to be applied contains relative source paths. If so, those relative source paths need to be rewritten relative to the SourceMap.

  If omitted, it is assumed that both SourceMaps are in the same directory, thus not needing any rewriting. (Supplying '.' has the same effect.)

SourceMapGenerator.prototype.toString()

Renders the source map being generated to a string.

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]]])

• line: The original line number associated with this source node, or null if it isn't associated with an original line.

• column: The original column number associated with this source node, or null if it isn't associated with an original column.

• source: The original source's filename; null if no filename is provided.

• chunk: Optional. Is immediately passed to SourceNode.prototype.add, see below.

• name: Optional. The original identifier.

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

Creates a SourceNode from generated code and a SourceMapConsumer.

• code: The generated code

• sourceMapConsumer The SourceMap for the generated code

• relativePath The optional path that relative sources in sourceMapConsumer should be relative to.

SourceNode.prototype.add(chunk)

Add a chunk of generated JS to this source node.

• chunk: A string snippet of generated JS code, another instance of SourceNode, or an array where each member is one of those things.

SourceNode.prototype.prepend(chunk)

Prepend a chunk of generated JS to this source node.

• chunk: A string snippet of generated JS code, another instance of SourceNode, or an array where each member is one of those things.

SourceNode.prototype.setSourceContent(sourceFile, sourceContent)

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

• sourceFile: The filename of the source file

• sourceContent: The content of the source file

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.

• fn: The traversal function.

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.

• fn: The traversal function.

SourceNode.prototype.join(sep)

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

• sep: The separator.

SourceNode.prototype.replaceRight(pattern, replacement)

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

• pattern: The pattern to replace.

• replacement: The thing to replace the pattern with.

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.

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.

Tests

Install NodeJS version 0.8.0 or greater, then run node test/run-tests.js.

To add new tests, create a new file named test/test-<your new test name>.js and export your test functions with names that start with "test", for example

exports["test doing the foo bar"] = function (assert, util) {
  ...
};

The new test will be located automatically when you run the suite.

The util argument is the test utility module located at test/source-map/util.

The assert argument is a cut down version of node's assert module. You have access to the following assertion functions:

• doesNotThrow

• equal

• ok

• strictEqual

• throws

(The reason for the restricted set of test functions is because we need the tests to run inside Firefox's test suite as well and so the assert module is shimmed in that environment. See build/assert-shim.js.)

Changelog

0.1.43

• Performance improvements for SourceMapGenerator and SourceNode. See issue #148 for some discussion and issues #150, #151, and #152 for implementations.