feat: add interopDefault util (#6)

README.md

@@ -316,6 +316,18 @@ console.log(toDataURL(`
 `))
 ```
 
+### `interopDefault`
+
+Return the default export of a module at the top-level, alongside any other named exports.
+
+```js
+// Assuming the shape { default: { foo: 'bar' }, baz: 'qux' }
+import myModule from 'my-module'
+
+// Returns { foo: 'bar', baz: 'qux' }
+console.log(interopDefault(myModule))
+```
+
 ## License
 
 MIT

lib/index.d.ts

@@ -69,3 +69,4 @@ export function fileURLToPath (id: URL | string) : string
 export function normalizeid (id: URL | string) : string
 export function loadURL (id: string) : Promise<string>
 export function toDataURL(code: string) : string
+export function interopDefault<T> (sourceModule: T): 'default' extends keyof T ? T['default'] : T

lib/index.mjs

@@ -107,6 +107,33 @@ export function createResolve (defaults) {
   }
 }
 
+export function interopDefault (sourceModule) {
+  if (!(sourceModule && 'default' in sourceModule)) {
+    return sourceModule
+  }
+  const newModule = sourceModule.default
+  for (const key in sourceModule) {
+    if (key === 'default') {
+      try {
+        Object.defineProperty(newModule, key, {
+          enumerable: false,
+          configurable: false,
+          get () { return newModule }
+        })
+      } catch (_err) {}
+    } else {
+      try {
+        Object.defineProperty(newModule, key, {
+          enumerable: true,
+          configurable: true,
+          get () { return sourceModule[key] }
+        })
+      } catch (_err) {}
+    }
+  }
+  return newModule
+}
+
 // Evaluate
 
 // TODO: Migrate to new Regexes

test/interop.test.mjs

@@ -0,0 +1,23 @@
+import { expect } from 'chai'
+import { interopDefault } from '../lib/index.mjs'
+
+const tests = [
+  [{}, {}],
+  [{ default: {} }, {}],
+  [{ default: { x: 2 } }, { x: 2 }],
+  [{ named: 2 }, { named: 2 }],
+  [{ named: 2, default: {} }, { named: 2 }],
+  [{ named: 1, default: { x: 2 } }, { named: 1, x: 2 }]
+]
+
+describe('interopDefault', () => {
+  for (const [input, result] of tests) {
+    it(JSON.stringify(input), () => {
+      const interop = interopDefault(input)
+      expect(interop).to.deep.equal(result)
+      if ('default' in input) {
+        expect(interop.default).to.deep.equal(result)
+      }
+    })
+  }
+})