add ts definition file (#9)

index.d.ts

@@ -0,0 +1,17 @@
+/**
+ * Rearranges items so that all items in the [left, k] are the smallest.
+ * The k-th element will have the (k - left + 1)-th smallest value in [left, right].
+ *
+ * @param arr the array to partially sort (in place)
+ * @param k middle index for partial sorting (as defined above)
+ * @param left left index of the range to sort (0 by default)
+ * @param right right index (last index of the array by default)
+ * @param compare compare function
+ */
+export default function quickselect<T>(
+    arr: T[],
+    k: number,
+    left?: number,
+    right?: number,
+    compare?: (x: T, y: T) => number
+): void;

package.json

@@ -28,8 +28,10 @@
   },
   "files": [
     "index.js",
+    "index.d.ts",
     "quickselect.js"
   ],
+  "types": "index.d.ts",
   "keywords": [
     "selection",
     "algorithm",