Example of custom Webpack plugin for embedding a build manifest inside your files at build-time. Customize to you needs.

inline-manifest-plugin.mjs

import { Compilation, sources } from 'webpack';

/**
 * This is a basic Webpack plugin producing an asset map similar to what WebpackManifestPlugin does,
 * except instead of emitting a manifest.json, it inlines the manifest in the source, replacing a
 * variable by name in the source.
 * It was written to only cover our basic use case of referencing some "internally public" chunks by
 * their basic name and map that to their built name with a hash.
 *
 * @example With an appropriate `filter` option, replaces a variable `__BUNDLING_MANIFEST__` with:
 * {
 *   "chunk.js": "chunk.a6bcf52794.js",
 *   "fonts.css": "fonts.ca87ad3290.css",
 *   "styles.css": "styles.6990fbe22c.css"
 * }
 */
export class InlineManifestPlugin {
  opts;

  constructor(opts = {}) {
    this.opts = {
      filter: opts.filter ?? (() => true),
      placeholder: opts.placeholder ?? '__BUNDLING_MANIFEST__',
    };
  }

  apply(compiler) {
    compiler.hooks.thisCompilation.tap('InlineManifestPlugin', (compilation) => {
      compilation.hooks.processAssets.tap(
        {
          name: 'InlineManifestPlugin',
          // https://webpack.js.org/api/compilation-hooks/#list-of-asset-processing-stages
          // Running early allows Terser to inline pre-compute expression, ex.
          // `__BUNDLING_MANIFEST__['styles.css']` → yields `'styles.hash.css'`
          stage: Compilation.PROCESS_ASSETS_STAGE_ADDITIONS,
        },
        () => {
          const manifest = {};

          for (const chunk of compilation.chunks.filter(this.opts.filter)) {
            for (const file of chunk.files) {
              manifest[`${chunk.name || chunk.id}${file.slice(file.lastIndexOf('.'))}`] = file;
            }
          }

          const manifestJson = JSON.stringify(manifest)
            // Replace double JSON quotes with single quotes so the text does not cause a syntax
            // error in dev mode where webpack wraps the code in eval("...").
            .replaceAll('"', '\'');

          // Iterate over all emitted assets and replace the placeholder in JS files.
          for (const asset of compilation.getAssets()) {
            if (!asset.name.endsWith('.js')) {
              continue;
            }

            const originalSource = asset.source;
            const sourceCode = originalSource.source();

            if (sourceCode.includes(this.opts.placeholder)) {
              // Use ReplaceSource to maintain source map compatibility.
              const replaceSource = new sources.ReplaceSource(originalSource);

              // Find all occurrences of the placeholder and replace them.
              let index = 0;
              do {
                index = sourceCode.indexOf(
                  this.opts.placeholder,
                  index + 1,
                );
                if (index !== -1) {
                  replaceSource.replace(
                    index,
                    index + this.opts.placeholder.length - 1,
                    manifestJson,
                  );
                }
              } while (index !== -1);

              compilation.updateAsset(asset.name, replaceSource);
            }
          }
        },
      );
    });
  }
}