source-map-url-modern

A maintained, dependency-free compatibility implementation of the archived source-map-url package.

This package intentionally remains a small regex wrapper. It is for existing code that needs the old API and output behavior on maintained Node.js and modern browsers. For new source-map transformation work, consider a library designed for that broader task.

Compatibility policy

The four methods and public regex preserve source-map-url 0.4.1 behavior. Changes are checked against a licensed copy of the original implementation, including exact returned strings, capture groups, match index, and regex state. Known regex quirks are retained rather than replaced with parser semantics.

See COMPATIBILITY.md for the complete matrix.

Installation

npm install source-map-url-modern

CommonJS

const sourceMappingURL = require("source-map-url-modern")

ESM

Node.js can import the CommonJS default without a second build:

import sourceMappingURL from "source-map-url-modern"

Browser global

Load source-map-url.js directly. The UMD bundle exposes window.sourceMappingURL.

<script src="source-map-url.js"></script>
<script>
  console.log(sourceMappingURL.getFrom("//# sourceMappingURL=app.js.map"))
</script>

AMD

The original anonymous UMD definition is preserved:

define(["source-map-url-modern"], function(sourceMappingURL) {
  return sourceMappingURL.existsIn("//# sourceMappingURL=app.js.map")
})

API

sourceMappingURL.getFrom(code)

Returns the URL from the first matching comment, "" for an empty URL, or null when there is no match.

sourceMappingURL.existsIn(code)

Returns whether a matching comment exists.

sourceMappingURL.removeFrom(code)

Removes the first matching comment and returns the exact resulting string.

sourceMappingURL.insertBefore(code, value)

Inserts value immediately before the first matching comment. If there is no match, appends value to code.

sourceMappingURL.regex

The same non-global regular expression exposed by 0.4.1. Its pattern, empty flags, two capture groups, match index, and lastIndex behavior are compatibility tested. Do not assume that it parses JavaScript or CSS; it intentionally matches compatible text patterns, including patterns inside string literals.

Migration from source-map-url

Change the dependency and require target:

- const sourceMappingURL = require("source-map-url")
+ const sourceMappingURL = require("source-map-url-modern")

To keep existing require("source-map-url") calls after this package is published, npm aliasing can map the old local dependency name to the new package:

{
  "dependencies": {
    "source-map-url": "npm:source-map-url-modern@^1.0.0"
  }
}

Support

• Node.js: maintained lines from Node.js 22 onward; CI covers 22, 24, and 26.
• Browsers: current Chromium, Firefox, and WebKit through Playwright.
• Runtime dependencies: zero.

Known differences

The runtime implementation has no intended behavioral differences from 0.4.1. Package name, metadata, supported environments, tests, CI, and documentation are modernized. The minimum supported Node.js version is explicit; the original package did not state one.

Development

npm test
npx playwright install
npm run test:browser
npm pack --dry-run

License

MIT. Original copyright is retained in LICENSE.