Don't attempt to compile modules whose source is null. Skip wasm/json. Resolves #7

lib/node-loader-babel.js

@@ -17,9 +17,21 @@ function isBabelConfigFile(filename) {
   );
 }
 
+// The formats that babel can compile
+// It cannot compile wasm/json
+const supportedModuleFormats = ["module", "commonjs"];
+
 export async function load(url, context, defaultLoad) {
   if (useLoader(url)) {
-    const { source } = await defaultLoad(url, context, defaultLoad);
+    const { source, format } = await defaultLoad(url, context, defaultLoad);
+
+    // NodeJS' implementation of defaultLoad returns a source of `null` for CommonJS modules.
+    // So we just skip compilation when it's commonjs until a future day when NodeJS (might) support that.
+    // Also, we skip compilation of wasm and json modules by babel, since babel isn't needed or possible
+    // in those situations
+    if (!source || (format && !supportedModuleFormats.includes(format))) {
+      return { source, format };
+    }
 
     const filename = urlModule.fileURLToPath(url);
     // Babel config files can themselves be ES modules,
@@ -32,7 +44,7 @@ export async function load(url, context, defaultLoad) {
     }
 
     const options = await loadOptionsAsync({
-      sourceType: "module",
+      sourceType: format || "module",
       root: process.cwd(),
       rootMode: "root",
       filename: filename,

test/commonjs.test.js

@@ -0,0 +1,15 @@
+import assert from "assert";
+
+describe("babel compilation of commonjs files", () => {
+  it(`can transform commonjs modules`, async () => {
+    const commonJSModule = await import("./fixtures/commonjs/main.cjs");
+
+    assert.deepEqual(commonJSModule.default, {
+      red: "#ff0000",
+      blue: "#0000ff",
+    });
+
+    assert.deepEqual(commonJSModule.red, "#ff0000");
+    assert.deepEqual(commonJSModule.blue, "#0000ff");
+  });
+});

test/fixtures/commonjs/main.cjs

@@ -0,0 +1,2 @@
+exports.red = "#ff0000";
+exports.blue = "#0000ff";

test/run-tests.js

@@ -3,6 +3,7 @@ import Mocha from "mocha";
 const mocha = new Mocha();
 
 mocha.addFile("./test/basic.test.js");
+mocha.addFile("./test/commonjs.test.js");
 
 mocha.loadFilesAsync().then(() => {
   mocha.run();