use live object to assign enumerable properties

.github/workflows/node.js.yml

@@ -18,7 +18,7 @@ jobs:
         # node-14's npm must be updated, but no longer updatable due to:
         #   https://github.com/npm/cli/issues/2663
         # because of this, node-14 test strategy is removed :(
-        node-version: [16.x, 18.x]
+        node-version: [16.x, 18.x, 19.x]
         os: [ubuntu-latest, windows-latest]
     steps:
     - uses: actions/checkout@v3

CHANGELOG.md

@@ -1,5 +1,8 @@
 # changelog
 
+ * 2.1.0 _Nov.29.2022_
+   * [add node v19](https://github.com/iambumblehead/esmock/pull/189) to ci-test pipeline
+   * [use live default export](https://github.com/iambumblehead/esmock/pull/189) to populate enumerable properties of mock definition
  * 2.0.9 _Nov.26.2022_
    * [resolve windows modules with correct drive letter](https://github.com/iambumblehead/esmock/pull/189) using [resolvewithplus patch](https://github.com/iambumblehead/resolvewithplus/pull/42) from @mshima
  * 2.0.8 _Nov.25.2022_

package.json

@@ -1,7 +1,7 @@
 {
   "name": "esmock",
   "type": "module",
-  "version": "2.0.9",
+  "version": "2.1.0",
   "license": "ISC",
   "readmeFilename": "README.md",
   "description": "provides native ESM import mocking for unit tests",

src/esmockModule.js

@@ -17,10 +17,20 @@ const isDirPathRe = /^\.?\.?([a-zA-Z]:)?(\/|\\)/
 const isMetaResolve = typeof import.meta.resolve === 'function'
 const nextId = ((id = 0) => () => ++id)()
 const asFileURL = p => p.startsWith('file://') ? p : url.pathToFileURL(p)
+const objProto = Object.getPrototypeOf({})
+const isPlainObj = o => Object.getPrototypeOf(o) === objProto
+
+// assigning the object to its own prototypal inheritor can error, eg
+//   'Cannot assign to read only property \'F_OK\' of object \'#<Object>\''
+// 
+// if not plain obj, assign enumerable vals only. core modules === plain obj
+const esmockModuleMerge = (defLive, def) => isPlainObj(defLive)
+  ? Object.assign({}, defLive, def)
+  : Object.assign(Object.keys(defLive).reduce(
+    (prev, k) => (prev[k] = defLive[k], prev), Object.create(defLive)), def)
 
 const esmockModuleMergeDefault = (defLive, def) =>
-  (isObj(defLive) && isObj(def))
-    ? Object.assign(Object.create(defLive), def) : def
+  (isObj(defLive) && isObj(def)) ? esmockModuleMerge(defLive, def) : def
 
 const esmockModuleApply = (defLive, def, fileURL) => {
   def = Object.assign({}, defLive || {}, {

tests/tests-mocha/src/app.js

@@ -11,6 +11,10 @@ if (typeof passport.initialize !== 'function') {
   throw new Error('inavalid mock')
 }
 
+if (!('_key' in passport)) {
+  throw new Error('inavalid mock, enumerable props not discoverable')
+}
+
 app.get('/', (req, res) => {
   res.send('Hello World!')
 })