feat: eval esm modules with fallback loader (#300)

src/eval.ts

@@ -125,20 +125,24 @@ export function evalModule(
 
   // Compile wrapped script
   let compiled;
+  const wrapped = wrapModule(source, { async: evalOptions.async });
   try {
-    compiled = vm.runInThisContext(
-      wrapModule(source, { async: evalOptions.async }),
-      {
-        filename,
-        lineOffset: 0,
-        displayErrors: false,
-      },
-    );
+    compiled = vm.runInThisContext(wrapped, {
+      filename,
+      lineOffset: 0,
+      displayErrors: false,
+    });
   } catch (error: any) {
-    if (ctx.opts.moduleCache) {
-      delete ctx.nativeRequire.cache[filename];
+    if (error.name === "SyntaxError" && evalOptions.async && ctx.nativeImport) {
+      // Support cases such as import.meta.[custom]
+      debug(ctx, "[esm]", "[import]", "[fallback]", filename);
+      compiled = esmEval(wrapped, ctx.nativeImport!);
+    } else {
+      if (ctx.opts.moduleCache) {
+        delete ctx.nativeRequire.cache[filename];
+      }
+      ctx.onError!(error);
     }
-    ctx.onError!(error);
   }
 
   // Evaluate module
@@ -182,3 +186,9 @@ export function evalModule(
 
   return evalOptions.async ? Promise.resolve(evalResult).then(next) : next();
 }
+
+function esmEval(code: string, nativeImport: (id: string) => Promise<any>) {
+  const uri = `data:text/javascript;base64,${Buffer.from(`export default ${code}`).toString("base64")}`;
+  return (...args: any[]) =>
+    nativeImport(uri).then((mod) => mod.default(...args));
+}

test/__snapshots__/fixtures.test.ts.snap

@@ -51,6 +51,8 @@ exports[`fixtures > hashbang > stdout 1`] = `"1"`;
 
 exports[`fixtures > import-map > stdout 1`] = `"{ alias: 'alias' }"`;
 
+exports[`fixtures > import-meta > stdout 1`] = `"hello! { hello: 'world' }"`;
+
 exports[`fixtures > json > stdout 1`] = `
 "Imported : { test: 123 } .default: { test: 123 }
 Imported with assertion : { test: 123 } .default: { test: 123 }

test/fixtures/import-meta/index.ts

@@ -0,0 +1,10 @@
+declare global {
+  interface ImportMeta {
+    custom: any;
+  }
+}
+
+import.meta.custom = { hello: "world" };
+console.log("hello!", import.meta.custom);
+
+export {};

test/fixtures/import-meta/package.json

@@ -0,0 +1,3 @@
+{
+  "type": "module"
+}