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Source Map

NPM

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

Use with Node

$ npm install source-map

Use on the Web

<script src="https://unpkg.com/source-map@0.7.3/dist/source-map.js"></script>
<script>
  sourceMap.SourceMapConsumer.initialize({
    "lib/mappings.wasm": "https://unpkg.com/source-map@0.7.3/lib/mappings.wasm",
  });
</script>

Table of Contents

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Examples

Consuming a source map

const 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",
};

const whatever = await SourceMapConsumer.with(rawSourceMap, null, consumer => {
  console.log(consumer.sources);
  // [ 'http://example.com/www/js/one.js',
  //   'http://example.com/www/js/two.js' ]

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

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

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

  return computeWhatever();
});

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.

SourceMapConsumer.initialize(options)

When using SourceMapConsumer outside of node.js, for example on the Web, it needs to know from what URL to load lib/mappings.wasm. You must inform it by calling initialize before constructing any SourceMapConsumers.

The options object has the following properties:

sourceMap.SourceMapConsumer.initialize({
  "lib/mappings.wasm": "https://example.com/source-map/lib/mappings.wasm",
});

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:

The promise of the constructed souce map consumer is returned.

When the SourceMapConsumer will no longer be used anymore, you must call its destroy method.

const consumer = await new sourceMap.SourceMapConsumer(rawSourceMapJsonData);
doStuffWith(consumer);
consumer.destroy();

Alternatively, you can use SourceMapConsumer.with to avoid needing to remember to call destroy.

SourceMapConsumer.with

Construct a new SourceMapConsumer from rawSourceMap and sourceMapUrl (see the SourceMapConsumer constructor for details. Then, invoke the async function f(SourceMapConsumer) -> T with the newly constructed consumer, wait for f to complete, call destroy on the consumer, and return f's return value.

You must not use the consumer after f completes!

By using with, you do not have to remember to manually call destroy on the consumer, since it will be called automatically once f completes.

const xSquared = await SourceMapConsumer.with(
  myRawSourceMap,
  null,
  async function (consumer) {
    // Use `consumer` inside here and don't worry about remembering
    // to call `destroy`.

    const x = await whatever(consumer);
    return x * x;
  }
);

// You may not use that `consumer` anymore out here; it has
// been destroyed. But you can use `xSquared`.
console.log(xSquared);

SourceMapConsumer.prototype.destroy()

Free this source map consumer's associated wasm data that is manually-managed.

consumer.destroy();

Alternatively, you can use SourceMapConsumer.with to avoid needing to remember to call destroy.

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)

Creates a new SourceMapGenerator from an existing SourceMapConsumer instance.

var generator = sourceMap.SourceMapGenerator.fromSourceMap(consumer);

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.

const consumer = await new SourceMapConsumer(
  fs.readFileSync("path/to/my-file.js.map", "utf8")
);
const 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] }