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.
Source Map
This is a library to generate and consume the source map format
described here.
Learn more here.
This library was written in the Asynchronous Module Definition
format. It should work in the following environments:
-
Modern Browsers (either after the build, or with an AMD loader such as
RequireJS)
-
Inside Firefox (as a JSM file, after the build)
-
With NodeJS versions 0.4.X
Installing with NPM (for use with NodeJS)
Simply
$ npm install source-map
Or, if you'd like to hack on this library and have it installed via npm so you
can try out your changes:
$ git clone https://fitzgen@github.com/mozilla/source-map.git
$ cd source-map
$ npm link .
Building from Source (for everywhere else)
Install NodeJS and Dryice. Then run node Makefile.dryice.js
. This should
create the following files:
-
dist/source-map.js
- The unminified browser version.
-
dist/source-map.min.js
- The minified browser version.
-
dist/SourceMapConsumer.jsm
- The JavaScript Module for inclusion in Firefox
source.
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/SourceMapConsumer.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.
-
mappings
: A string of base64 VLQs which contain the actual mappings.
-
file
: The generated filename this source map is associated with.
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:
-
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.
SourceMapGenerator
An instance of the SourceMapGenerator represents a source map which is being
built incrementally.
new SourceMapGenerator(startOfSourceMap)
To create a new one, you must pass an object with the following properties:
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.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])
-
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.
-
chunk
: Optional. Is immediately passed to SourceNode.prototype.add
, see
below.
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.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.join(sep)
Like Array.prototype.join
except for SourceNodes. Inserts the separator
between each of this source node's children.
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.
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 0.4.0 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 () {
...
};
The new test will be located automatically when you run the suite.