Add isArray

package.json

@@ -1,6 +1,6 @@
 {
     "name": "@glideapps/ts-necessities",
-    "version": "2.2.2",
+    "version": "2.2.3",
     "description": "Small utilities to make life with TypeScript easier",
     "main": "dist/index.js",
     "types": "dist/index.d.ts",

src/index.ts

@@ -108,6 +108,27 @@ export function isEnumValue<T extends object>(e: T, x: unknown): x is T[keyof T]
     return (Object.keys(e) as Array<keyof T>).map(k => e[k]).some(v => v === (x as T[keyof T]));
 }
 
+/**
+ * Returns whether `x` is an array.
+ *
+ * We have this because `Array.isArray(x)` returns `x is any[]`, which means
+ * that this code compiles without error, for example:
+ *
+ * ```typescript
+ * function thisShouldNotCompile(x: string | readonly string[]) {
+ *     if (Array.isArray(x)) {
+ *         const s = x[0];
+ *         s.thisIsAnAny("but it's actually a string");
+ *     }
+ * }
+ * ```
+ */
+export function isArray<T, U>(x: readonly T[] | U): x is readonly T[];
+export function isArray<T, U>(x: T[] | U): x is T[];
+export function isArray<T, U>(x: readonly T[] | U): x is readonly T[] {
+    return Array.isArray(x);
+}
+
 /**
  * Returns whether `obj` has `name` as its own property.
  */