convert-source-map

What is convert-source-map?

The convert-source-map npm package is used for dealing with inline and external source maps. It provides functionalities to convert source maps between different formats, such as from a JSON object to a base64-encoded string or from a base64-encoded string to a JSON object. It can also add and remove source map comments from files or code strings.

What are convert-source-map's main functionalities?

Convert source map from JSON to base64

This feature allows you to convert a source map from a JSON object to a base64-encoded string, which can be appended to a file as an inline source map.

const convert = require('convert-source-map');
const sourceMap = { version: 3, file: 'out.js', sources: ['foo.js', 'bar.js'], names: [], mappings: 'AAgBC' };
const base64Map = convert.fromObject(sourceMap).toBase64();

Convert source map from base64 to JSON

This feature allows you to convert a base64-encoded source map string back into a JSON object for further manipulation or analysis.

const convert = require('convert-source-map');
const base64Map = 'eyJ2ZXJzaW9uIjozLCJmaWxlIjoib3V0LmpzIiwic291cmNlcyI6WyJmb28uanMiLCJiYXIuanMiXSwibmFtZXMiOltdLCJtYXBwaW5ncyI6IkFBZ0JDIn0=';
const sourceMap = convert.fromBase64(base64Map).toObject();

Add source map comment to code

This feature enables you to append a source map comment to a string of code, which can be useful when generating code dynamically.

const convert = require('convert-source-map');
const code = 'function foo() {}';
const sourceMap = convert.fromObject({ version: 3, sources: ['foo.js'], names: [], mappings: 'AAAA' });
const codeWithSourceMap = code + '\n' + sourceMap.toComment();

Remove source map comment from code

This feature allows you to remove source map comments from a string of code, which can be useful when you need to process the code further without the source map.

const convert = require('convert-source-map');
const codeWithSourceMap = 'function foo() {}\n//# sourceMappingURL=data:application/json;base64,eyJ2ZXJzaW9uIjozLCJzb3VyY2VzIjpbImZvby5qcyJdLCJuYW1lcyI6W10sIm1hcHBpbmdzIjoiQUFBQSJ9';
const codeWithoutSourceMap = convert.removeComments(codeWithSourceMap);

Other packages similar to convert-source-map

source-map

The 'source-map' package provides functionalities to generate and consume source maps. It allows for more complex manipulation of source maps compared to 'convert-source-map', such as applying mappings from one source map to another.

source-map-support

The 'source-map-support' package adds source map support to stack traces in node.js. It is more focused on using source maps to improve debugging rather than converting or manipulating source maps.

sourcemap-codec

The 'sourcemap-codec' package is a library for encoding and decoding the mappings field of source maps. It is more specialized and lower-level compared to 'convert-source-map', focusing solely on the mappings aspect of source maps.

README

convert-source-map

Converts a source-map from/to different formats and allows adding/changing properties.

var convert = require('convert-source-map');

var json = convert
  .fromComment('//# sourceMappingURL=data:application/json;base64,eyJ2ZXJzaW9uIjozLCJmaWxlIjoiYnVpbGQvZm9vLm1pbi5qcyIsInNvdXJjZXMiOlsic3JjL2Zvby5qcyJdLCJuYW1lcyI6W10sIm1hcHBpbmdzIjoiQUFBQSIsInNvdXJjZVJvb3QiOiIvIn0=')
  .toJSON();

var modified = convert
  .fromComment('//# sourceMappingURL=data:application/json;base64,eyJ2ZXJzaW9uIjozLCJmaWxlIjoiYnVpbGQvZm9vLm1pbi5qcyIsInNvdXJjZXMiOlsic3JjL2Zvby5qcyJdLCJuYW1lcyI6W10sIm1hcHBpbmdzIjoiQUFBQSIsInNvdXJjZVJvb3QiOiIvIn0=')
  .setProperty('sources', [ 'SRC/FOO.JS' ])
  .toJSON();

console.log(json);
console.log(modified);

{"version":3,"file":"build/foo.min.js","sources":["src/foo.js"],"names":[],"mappings":"AAAA","sourceRoot":"/"}
{"version":3,"file":"build/foo.min.js","sources":["SRC/FOO.JS"],"names":[],"mappings":"AAAA","sourceRoot":"/"}

Upgrading

Prior to v2.0.0, the fromMapFileComment and fromMapFileSource functions took a String directory path and used that to resolve & read the source map file from the filesystem. However, this made the library limited to nodejs environments and broke on sources with querystrings.

In v2.0.0, you now need to pass a function that does the file reading. It will receive the source filename as a String that you can resolve to a filesystem path, URL, or anything else.

If you are using convert-source-map in nodejs and want the previous behavior, you'll use a function like such:

+ var fs = require('fs'); // Import the fs module to read a file
+ var path = require('path'); // Import the path module to resolve a path against your directory
- var conv = convert.fromMapFileSource(css, '../my-dir');
+ var conv = convert.fromMapFileSource(css, function (filename) {
+   return fs.readFileSync(path.resolve('../my-dir', filename), 'utf-8');
+ });

API

fromObject(obj)

Returns source map converter from given object.

fromJSON(json)

Returns source map converter from given json string.

fromURI(uri)

Returns source map converter from given uri encoded json string.

fromBase64(base64)

Returns source map converter from given base64 encoded json string.

fromComment(comment)

Returns source map converter from given base64 or uri encoded json string prefixed with //# sourceMappingURL=....

fromMapFileComment(comment, readMap)

Returns source map converter from given filename by parsing //# sourceMappingURL=filename.

readMap must be a function which receives the source map filename and returns either a String or Buffer of the source map (if read synchronously), or a Promise containing a String or Buffer of the source map (if read asynchronously).

If readMap doesn't return a Promise, fromMapFileComment will return a source map converter synchronously.

If readMap returns a Promise, fromMapFileComment will also return Promise. The Promise will be either resolved with the source map converter or rejected with an error.

Examples

Synchronous read in Node.js:

var convert = require('convert-source-map');
var fs = require('fs');

function readMap(filename) {
  return fs.readFileSync(filename, 'utf8');
}

var json = convert
  .fromMapFileComment('//# sourceMappingURL=map-file-comment.css.map', readMap)
  .toJSON();
console.log(json);

Asynchronous read in Node.js:

var convert = require('convert-source-map');
var { promises: fs } = require('fs'); // Notice the `promises` import

function readMap(filename) {
  return fs.readFile(filename, 'utf8');
}

var converter = await convert.fromMapFileComment('//# sourceMappingURL=map-file-comment.css.map', readMap)
var json = converter.toJSON();
console.log(json);

Asynchronous read in the browser:

var convert = require('convert-source-map');

async function readMap(url) {
  const res = await fetch(url);
  return res.text();
}

const converter = await convert.fromMapFileComment('//# sourceMappingURL=map-file-comment.css.map', readMap)
var json = converter.toJSON();
console.log(json);

fromSource(source)

Finds last sourcemap comment in file and returns source map converter or returns null if no source map comment was found.

fromMapFileSource(source, readMap)

Finds last sourcemap comment in file and returns source map converter or returns null if no source map comment was found.

readMap must be a function which receives the source map filename and returns either a String or Buffer of the source map (if read synchronously), or a Promise containing a String or Buffer of the source map (if read asynchronously).

If readMap doesn't return a Promise, fromMapFileSource will return a source map converter synchronously.

If readMap returns a Promise, fromMapFileSource will also return Promise. The Promise will be either resolved with the source map converter or rejected with an error.

toObject()

Returns a copy of the underlying source map.

toJSON([space])

Converts source map to json string. If space is given (optional), this will be passed to JSON.stringify when the JSON string is generated.

toURI()

Converts source map to uri encoded json string.

toBase64()

Converts source map to base64 encoded json string.

toComment([options])

Converts source map to an inline comment that can be appended to the source-file.

By default, the comment is formatted like: //# sourceMappingURL=..., which you would normally see in a JS source file.

When options.encoding == 'uri', the data will be uri encoded, otherwise they will be base64 encoded.

When options.multiline == true, the comment is formatted like: /*# sourceMappingURL=... */, which you would find in a CSS source file.

addProperty(key, value)

Adds given property to the source map. Throws an error if property already exists.

setProperty(key, value)

Sets given property to the source map. If property doesn't exist it is added, otherwise its value is updated.

getProperty(key)

Gets given property of the source map.

removeComments(src)

Returns src with all source map comments removed

removeMapFileComments(src)

Returns src with all source map comments pointing to map files removed.

commentRegex

Provides a fresh RegExp each time it is accessed. Can be used to find source map comments.

Breaks down a source map comment into groups: Groups: 1: media type, 2: MIME type, 3: charset, 4: encoding, 5: data.

mapFileCommentRegex

Provides a fresh RegExp each time it is accessed. Can be used to find source map comments pointing to map files.

generateMapFileComment(file, [options])

Returns a comment that links to an external source map via file.

By default, the comment is formatted like: //# sourceMappingURL=..., which you would normally see in a JS source file.

When options.multiline == true, the comment is formatted like: /*# sourceMappingURL=... */, which you would find in a CSS source file.