feat: support importing type module dependencies (#18)

Closes #17

src/node.ts

@@ -3,6 +3,8 @@ import type { RawSourceMap } from 'source-map'
 import sourceMapSupport from 'source-map-support'
 import { transformSync, TransformOptions } from 'esbuild'
 import { addHook } from 'pirates'
+import fs from 'fs';
+import module from 'module';
 import { getOptions, inferPackageFormat } from './options'
 
 const map: { [file: string]: string | RawSourceMap } = {}
@@ -23,6 +25,34 @@ function installSourceMapSupport() {
   })
 }
 
+type COMPILE = (code: string, filename: string, format?: 'cjs' | 'esm') => string
+
+/**
+ * Patch the Node CJS loader to suppress the ESM error
+ * https://github.com/nodejs/node/blob/069b5df/lib/internal/modules/cjs/loader.js#L1125
+ * 
+ * As per https://github.com/standard-things/esm/issues/868#issuecomment-594480715
+ */
+function patchCommonJsLoader(compile: COMPILE) {
+  // @ts-expect-error
+  const extensions = module.Module._extensions;
+  const jsHandler = extensions['.js'];
+
+  extensions['.js'] = function(module: any, filename: string) {
+    try {
+      return jsHandler.call(this, module, filename)
+    } catch (error) {
+      if (error.code !== 'ERR_REQUIRE_ESM') {
+        throw error;
+      }
+
+      let content = fs.readFileSync(filename, 'utf8');
+      content = compile(content, filename, 'cjs');
+      module._compile(content, filename);
+    }
+  };
+}
+
 type LOADERS = 'js' | 'jsx' | 'ts' | 'tsx'
 const FILE_LOADERS = {
   '.js': 'js',
@@ -44,10 +74,10 @@ export function register(
 ) {
   const { extensions = DEFAULT_EXTENSIONS, ...overrides } = esbuildOptions
 
-  function compile(code: string, filename: string) {
+  const compile: COMPILE = function compile(code, filename, format) {
     const dir = dirname(filename)
     const options = getOptions(dir)
-    const format = inferPackageFormat(dir, filename)
+    format = format ?? inferPackageFormat(dir, filename)
 
     const { code: js, warnings, map: jsSourceMap } = transformSync(code, {
       sourcefile: filename,
@@ -69,6 +99,7 @@ export function register(
     return js
   }
   installSourceMapSupport()
+  patchCommonJsLoader(compile)
   addHook(compile, {
     exts: extensions,
   })

tests/import-type-module/index.js

@@ -0,0 +1,3 @@
+import foo from 'foo'
+
+console.log(foo)

tests/import-type-module/package.json

@@ -0,0 +1,3 @@
+{
+  "private": true
+}

tests/test.ts

@@ -38,4 +38,13 @@ test('package type module', async () => {
   assert.is(stdout, 'foo')
 })
 
+test('import type module', async () => {
+  const { stdout } = await execa('node', [
+    '-r',
+    `${process.cwd()}/register.js`,
+    `${process.cwd()}/tests/import-type-module/index.js`,
+  ])
+  assert.is(stdout, 'foo')
+})
+
 test.run()