source-map-loader

What is source-map-loader?

The source-map-loader package is used to load source map data from existing source files. It extracts source maps from the source files (like JavaScript files) when they are included in the webpack build process. This allows for better debugging capabilities because the browser developer tools can map the generated code back to the original source code, which is particularly useful when working with transpiled languages or minified code.

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

Extracting source maps

This webpack configuration snippet demonstrates how to use source-map-loader to extract source maps from JavaScript files before they are processed by other loaders. The 'enforce: pre' property ensures that the source-map-loader runs before other loaders.

module.exports = {
  module: {
    rules: [
      {
        test: /\.js$/,
        use: ['source-map-loader'],
        enforce: 'pre'
      }
    ]
  }
};

Other packages similar to source-map-loader

source-map-support

The source-map-support package provides source map support for stack traces in node applications. It allows error stack traces to be translated back to the original source code. Unlike source-map-loader, which is used during the build process, source-map-support is used at runtime.

babel-loader

The babel-loader is a webpack loader that transpiles JavaScript files using Babel and can optionally generate source maps. While it serves a different primary purpose (transpilation), the generation of source maps is a feature that overlaps with source-map-loader's functionality.

css-loader

The css-loader interprets `@import` and `url()` like import/require() and resolves them. It can also generate source maps for CSS files, which is a feature that is somewhat similar to what source-map-loader does for JavaScript files.

README

source-map-loader

Extracts source maps from existing source files (from their sourceMappingURL).

Getting Started

To begin, you'll need to install source-map-loader:

npm i -D source-map-loader

Then add the plugin to your webpack config. For example:

file.js

import css from "file.css";

webpack.config.js

module.exports = {
  module: {
    rules: [
      {
        test: /\.js$/,
        enforce: "pre",
        use: ["source-map-loader"],
      },
    ],
  },
};

The source-map-loader extracts existing source maps from all JavaScript entries. This includes both inline source maps as well as those linked via URL. All source map data is passed to webpack for processing as per a chosen source map style specified by the devtool option in webpack.config.js. This loader is especially useful when using 3rd-party libraries having their own source maps. If not extracted and processed into the source map of the webpack bundle, browsers may misinterpret source map data. source-map-loader allows webpack to maintain source map data continuity across libraries so ease of debugging is preserved. The source-map-loader will extract from any JavaScript file, including those in the node_modules directory. Be mindful in setting include and exclude rule conditions to maximize bundling performance.

And run webpack via your preferred method.

Options

Name	Type	Default	Description
filterSourceMappingUrl	{Function}	undefined	Allows to control SourceMappingURL behaviour

filterSourceMappingUrl

Type: Function Default: undefined

Allows you to specify the behavior of the loader for SourceMappingURL comment.

The function must return one of the values:

• true or 'consume' - consume the source map and remove SourceMappingURL comment (default behavior)
• false or 'remove' - do not consume the source map and remove SourceMappingURL comment
• skip - do not consume the source map and do not remove SourceMappingURL comment

Example configuration:

webpack.config.js

module.exports = {
  module: {
    rules: [
      {
        test: /\.js$/,
        enforce: "pre",
        use: [
          {
            loader: "source-map-loader",
            options: {
              filterSourceMappingUrl: (url, resourcePath) => {
                if (/broker-source-map-url\.js$/i.test(url)) {
                  return false;
                }

                if (/keep-source-mapping-url\.js$/i.test(resourcePath)) {
                  return "skip";
                }

                return true;
              },
            },
          },
        ],
      },
    ],
  },
};

Examples

Ignoring Warnings

To ignore warnings, you can use the following configuration:

webpack.config.js

module.exports = {
  module: {
    rules: [
      {
        test: /\.js$/,
        enforce: "pre",
        use: ["source-map-loader"],
      },
    ],
  },
  ignoreWarnings: [/Failed to parse source map/],
};

More information about the ignoreWarnings option can be found here

Contributing

Please take a moment to read our contributing guidelines if you haven't yet done so.

CONTRIBUTING

License

MIT

Changelog

2.0.0 (2020-12-24)

⚠ BREAKING CHANGES

• minimum supported webpack version is 5