fix: correctly narrow return type of isArray for {} arguments (#470)

README.md

@@ -13,35 +13,38 @@ Function documentation available [here](https://alcalzone.github.io/shared-utils
 <!--
 	Placeholder for the next version (at the beginning of the line):
 	### __WORK IN PROGRESS__
--->
+-->
+### __WORK IN PROGRESS__
+* Fix: correctly narrow return type of isArray for `{}` arguments
+
 ### 4.0.4 (2022-09-07)
-* Fix: narrowed type for `isArray` is inferred correctly for `readonly` arrays
-
+* Fix: narrowed type for `isArray` is inferred correctly for `readonly` arrays
+
 ### 4.0.3 (2022-08-27)
-* Update `isArray` to be compatible with TS 4.8 changes
-
+* Update `isArray` to be compatible with TS 4.8 changes
+
 ### 4.0.1 (2021-11-15)
-`SortedQueue`: Fixed an issue where inserting an item before the first one would cause the queue to lose track of items
-
+`SortedQueue`: Fixed an issue where inserting an item before the first one would cause the queue to lose track of items
+
 ### 4.0.0 (2021-06-19)
-* Node.js 12+ is now required
-
+* Node.js 12+ is now required
+
 ### 3.0.4 (2021-04-24)
 * Fix compatibility of `wait()` with Electron if `unref` is `true`
-* Dependency updates
-
+* Dependency updates
+
 ### 3.0.3 (2021-03-09)
 #### Fixes
-* Fixed compatibility with TypeScript 4.2
-
+* Fixed compatibility with TypeScript 4.2
+
 ### 3.0.2 (2021-01-16)
 #### Fixes
-* The argument to `resolve` of `DeferredPromise` is no longer optional, except for `Promise<void>`
-
+* The argument to `resolve` of `DeferredPromise` is no longer optional, except for `Promise<void>`
+
 ### 3.0.1 (2020-12-05)
 #### Fixes
-* The typeguard `isObject` no longer narrows the type of the argument to `object`
-
+* The typeguard `isObject` no longer narrows the type of the argument to `object`
+
 ### 3.0.0 (2020-08-16)
 #### Breaking changes
 * Renamed the following types:
@@ -66,7 +69,7 @@ Function documentation available [here](https://alcalzone.github.io/shared-utils
 
 #### Fixes
 * The type `CallbackAPIReturnType` now works with `strictNullChecks`.
-* The type `Promisify` is no longer experimental and no longer messes up the inferred signature argument names
-
+* The type `Promisify` is no longer experimental and no longer messes up the inferred signature argument names
+
 ### 2.3.0 (2020-06-08)
 * Added optional `unref` parameter to `async` -> `wait(ms, [unref])`

build/typeguards/index.d.ts

@@ -5,7 +5,7 @@
 export declare function isObject<T>(it: T): it is T & Record<string, unknown>;
 declare type IfAny<T, Y, N> = 0 extends (1 & T) ? Y : N;
 declare type IsAny<T> = IfAny<T, true, never>;
-declare type ExtractArray<T> = true extends IsAny<T> ? unknown[] : T extends readonly unknown[] ? T : unknown extends T ? (T & unknown[]) : never;
+declare type ExtractArray<T> = true extends IsAny<T> ? unknown[] : T extends readonly unknown[] ? T : {} extends T ? (T & unknown[]) : never;
 /**
  * Tests whether the given variable is really an Array
  * @param it The variable to test

src/typeguards/index.ts

@@ -14,10 +14,10 @@ type IfAny<T, Y, N> = 0 extends (1 & T) ? Y : N;
 type IsAny<T> = IfAny<T, true, never>;
 
 type ExtractArray<T> =
-		true extends IsAny<T> ? unknown[]
-		: T extends readonly unknown[] ? T
-		: unknown extends T ? (T & unknown[])
-		: never;
+	true extends IsAny<T> ? unknown[]
+	: T extends readonly unknown[] ? T
+	: {} extends T ? (T & unknown[])
+	: never;
 
 /**
  * Tests whether the given variable is really an Array

src/typeguards/typeguards.test.ts

@@ -93,6 +93,7 @@ describe("lib/typeguards =>", () => {
 			const _number = _unknown as number;
 			const _numberArray = _unknown as number[];
 			const _readonlyNumberArray = _unknown as readonly number[];
+			const _nonNullish = _unknown as {};
 
 			if (isArray(_any)) {
 				assertTrue<Equals<typeof _any, any>>();
@@ -131,6 +132,12 @@ describe("lib/typeguards =>", () => {
 				_readonlyNumberArray;
 				// ^?
 			}
+
+			if (isArray(_nonNullish)) {
+				assertTrue<Equals<typeof _nonNullish, unknown[]>>();
+				_nonNullish;
+				// ^?
+			}
 		});
 	});
 });