fix(hasConfigurableGlobal): handle existing globals with undefined va…

…lue (#669)

Co-authored-by: Artem Zakharchenko <[email protected]>

src/utils/hasConfigurableGlobal.test.ts

@@ -26,6 +26,30 @@ it('returns false if the global property does not exist', () => {
   expect(hasConfigurableGlobal('_non-existing')).toBe(false)
 })
 
+it('returns false for existing global with undefined as a value', () => {
+  Object.defineProperty(global, '_existsAndUndefined', {
+    value: undefined,
+    configurable: true,
+  })
+  expect(hasConfigurableGlobal('_existsAndUndefined')).toBe(false)
+})
+
+it('returns false for existing global with null as a value', () => {
+  Object.defineProperty(global, '_existsAndNull', {
+    value: null,
+    configurable: true,
+  })
+  expect(hasConfigurableGlobal('_existsAndNull')).toBe(false)
+})
+
+it('returns false for existing global with a getter that returns undefined', () => {
+  Object.defineProperty(global, '_existsGetterUndefined', {
+    get: () => undefined,
+    configurable: true,
+  })
+  expect(hasConfigurableGlobal('_existsGetterUndefined')).toBe(false)
+})
+
 it('returns false and prints an error for implicitly non-configurable global property', () => {
   Object.defineProperty(global, '_implicitlyNonConfigurable', {
     value: 'something',

src/utils/hasConfigurableGlobal.ts

@@ -5,10 +5,24 @@
 export function hasConfigurableGlobal(propertyName: string): boolean {
   const descriptor = Object.getOwnPropertyDescriptor(globalThis, propertyName)
 
+  // The property is not set at all.
   if (typeof descriptor === 'undefined') {
     return false
   }
 
+  // The property is set to a getter that returns undefined.
+  if (
+    typeof descriptor.get === 'function' &&
+    typeof descriptor.get() === 'undefined'
+  ) {
+    return false
+  }
+
+  // The property is set to a value equal to undefined.
+  if (typeof descriptor.get === 'undefined' && descriptor.value == null) {
+    return false
+  }
+
   if (typeof descriptor.set === 'undefined' && !descriptor.configurable) {
     console.error(
       `[MSW] Failed to apply interceptor: the global \`${propertyName}\` property is non-configurable. This is likely an issue with your environment. If you are using a framework, please open an issue about this in their repository.`