Improve CJS/ESM interoperability support

See [#345][0].

[0]: #345

.npmignore

@@ -8,7 +8,7 @@
 !README.md
 !SECURITY.md
 
-!dist/index.cjs
-!dist/index.d.ts
-!dist/index.js
-!dist/middlewares/**/*.d.ts
+!dist/cjs/index.js
+!dist/cjs/package.json
+!dist/esm/index.js
+!dist/types/**/*.d.ts

bin/build-helmet.js

@@ -1,38 +1,61 @@
 #!/usr/bin/env node
+import { promises as fs } from "fs";
 import * as path from "path";
 import { fileURLToPath } from "url";
 import rollupTypescript from "@rollup/plugin-typescript";
-import { writeRollup, withCommonJsFile } from "./helpers.js";
+import {
+  withCommonJsFile,
+  withEsmFile,
+  writeRollup
+} from "./helpers.js";
 
 const thisPath = fileURLToPath(import.meta.url);
 const rootPath = path.join(path.dirname(thisPath), "..");
+const distPath = path.join(rootPath, "dist");
 const esmSourcePath = path.join(rootPath, "index.ts");
-const esmDistPath = path.join(rootPath, "dist", "index.js");
-const commonJsDistPath = path.join(rootPath, "dist", "index.cjs");
+const esmDistDir = path.join(distPath, "esm");
+const esmDistPath = path.join(esmDistDir, "index.js");
+const commonJsDistDir = path.join(distPath, "cjs");
+const commonJsDistPath = path.join(commonJsDistDir, "index.js");
+const typesDistDir = path.join(distPath, "types");
 
 const compileEsm = () =>
-  writeRollup(
-    {
-      input: esmSourcePath,
-      plugins: [rollupTypescript({ tsconfig: "./tsconfig-esm.json" })],
-    },
-    { file: esmDistPath }
-  );
+  withEsmFile(esmSourcePath, async (esmTempPath) => {
+    await writeRollup(
+      {
+        input: esmTempPath,
+        plugins: [rollupTypescript({ tsconfig: "./tsconfig-esm.json" })],
+      },
+      { file: path.join(distPath, "index.js") }
+      );
+
+    await fs.mkdir(esmDistDir);
+    await fs.rename(path.join(distPath, "index.js"), esmDistPath);
+    await fs.rename(path.join(typesDistDir, "tmp-esm-index.d.ts"), path.join(typesDistDir, "index.d.ts"));
+  });
 
 const compileCommonjs = () =>
-  withCommonJsFile(esmSourcePath, (commonJsSourcePath) =>
-    writeRollup(
+  withCommonJsFile(esmSourcePath, async (commonJsTempPath) => {
+    await writeRollup(
       {
-        input: commonJsSourcePath,
+        input: commonJsTempPath,
         plugins: [rollupTypescript({ tsconfig: "./tsconfig-commonjs.json" })],
       },
       {
-        exports: "default",
+        exports: "named",
         file: commonJsDistPath,
         format: "cjs",
-      }
-    )
-  );
+      });
+
+    const cjsPackageJson = JSON.stringify({
+      type: "commonjs",
+    });
+
+    await fs.writeFile(
+      path.join(commonJsDistDir, "package.json"),
+      cjsPackageJson
+    );
+  });
 
 async function main() {
   await compileEsm();

bin/helpers.js

@@ -8,23 +8,62 @@ export async function writeRollup(inputOptions, outputOptions) {
   await bundle.close();
 }
 
+export async function withEsmFile(esmSourcePath, fn) {
+  const esmTempPath = path.join(
+    path.dirname(esmSourcePath),
+    "tmp-esm-index.ts"
+  );
+
+  const lines = (await fs.readFile(esmSourcePath, "utf8")).split(/\r?\n/);
+  const startLineCjsFence = lines.findIndex((line) =>
+    line.includes("!helmet-start-of-commonjs-exports")
+  );
+  const endLineCjsFence = lines.findIndex((line) =>
+    line.includes("!helmet-end-of-commonjs-exports")
+  );
+  const lineCount = endLineCjsFence - startLineCjsFence + 2;
+  lines.splice(startLineCjsFence, lineCount);
+
+  const startLineEsmFence = lines.findIndex((line) =>
+    line.includes("!helmet-start-of-esm-exports")
+  );
+  lines.splice(startLineEsmFence, 1);
+
+  const endLineEsmFence = lines.findIndex((line) =>
+    line.includes("!helmet-end-of-esm-exports")
+  );
+  lines.splice(endLineEsmFence, 1);
+
+  try {
+    await fs.writeFile(esmTempPath, lines.join("\n"));
+
+    await fn(esmTempPath);
+  } finally {
+    await fs.unlink(esmTempPath);
+  }
+}
+
 export async function withCommonJsFile(esmSourcePath, fn) {
-  const commonJsSourcePath = path.join(
+  const commonJsTempPath = path.join(
     path.dirname(esmSourcePath),
     "tmp-commonjs-index.ts"
   );
 
   const lines = (await fs.readFile(esmSourcePath, "utf8")).split(/\r?\n/);
-  const resultLines = lines.slice(
-    0,
-    lines.findIndex((line) => line.includes("!helmet-end-of-commonjs"))
+  const startLine = lines.findIndex((line) =>
+    line.includes("!helmet-start-of-commonjs-exports")
+  );
+  const endLine = lines.findIndex((line) =>
+    line.includes("!helmet-end-of-commonjs-exports")
   );
+  lines.splice(startLine, 1);
+  const resultLines = lines.slice(0, endLine - 1);
 
   try {
-    await fs.writeFile(commonJsSourcePath, resultLines.join("\n"));
+    await fs.writeFile(commonJsTempPath, resultLines.join("\n"));
 
-    await fn(commonJsSourcePath);
+    await fn(commonJsTempPath);
   } finally {
-    await fs.unlink(commonJsSourcePath);
+    await fs.unlink(commonJsTempPath);
   }
 }

index.ts

@@ -273,8 +273,12 @@ const helmet: Helmet = Object.assign(
 
 export default helmet;
 
-// !helmet-end-of-commonjs
+// !helmet-start-of-commonjs-exports
+exports = helmet;
+module.exports = helmet;
+// !helmet-end-of-commonjs-exports
 
+// !helmet-start-of-esm-exports
 export {
   contentSecurityPolicy,
   crossOriginEmbedderPolicy,
@@ -292,3 +296,4 @@ export {
   xPoweredBy as hidePoweredBy,
   xXssProtection as xssFilter,
 };
+// !helmet-end-of-esm-exports

package.json

@@ -54,13 +54,14 @@
   },
   "license": "MIT",
   "type": "module",
-  "types": "./dist/index.d.ts",
-  "main": "./dist/index.cjs",
+  "main": "./dist/cjs/index.js",
+  "module": "./dist/esm/index.js",
+  "types": "./dist/types/index.d.ts",
   "exports": {
     ".": {
-      "import": "./dist/index.js",
-      "require": "./dist/index.cjs",
-      "types": "./dist/index.d.ts"
+      "import": "./dist/esm/index.js",
+      "require": "./dist/cjs/index.js",
+      "types": "./dist/types/index.d.ts"
     }
   }
 }

tsconfig-esm.json

@@ -1,9 +1,8 @@
 {
   "extends": "./tsconfig",
-  "exclude": ["dist"],
   "compilerOptions": {
-    "outDir": "dist",
     "declaration": true,
-    "declarationDir": "."
-  }
+    "declarationDir": "types"
+  },
+  "include": ["tmp-esm-index.ts"]
 }

tsconfig.json

@@ -9,6 +9,8 @@
     "noUnusedParameters": true,
     "noUncheckedIndexedAccess": true,
     "strict": true,
-    "target": "es6"
-  }
+    "target": "es6",
+    "outDir": "."
+  },
+  "exclude": ["node_modules", "bin", "dist"]
 }