refactor: add tests

package.json

@@ -13,6 +13,7 @@
   "scripts": {
     "prepublishOnly": "pnpm run build && echo 'Run the npm publish command inside `dist`.' && exit 1",
     "build": "rimraf dist && tsc && node ./scripts/package.js",
+    "test": "vitest",
     "lint": "eslint --ext .ts,.tsx,.js,.mjs . && prettier --check .",
     "lint:fix": "eslint --ext .ts,.tsx,.js,.mjs . --fix && prettier -w ."
   },
@@ -32,7 +33,7 @@
   "devDependencies": {
     "@typescript-eslint/eslint-plugin": "^6.4.0",
     "@typescript-eslint/parser": "^6.4.0",
-    "@vitest/coverage-c8": "^0.33.0",
+    "@vitest/coverage-v8": "^0.34.1",
     "eslint": "^8.47.0",
     "eslint-config-prettier": "^8.10.0",
     "eslint-plugin-import": "^2.27.5",

src/array.ts

@@ -117,7 +117,7 @@ export const lastIndex = <T>(
  *
  * @param arr - An array
  * @param predicate - A predicate function.
- * @param thisArg - If provided, it will be used as the this value for each invocation of predicate. If it is not provided, `undefined` is used instead.
+ * @param thisArg - If provided, it will be used as the this value for each invocation of predicate. If it is not provided, the first element is returned.
  * @returns The first item that matches the predicate, or `None` if no item matches.
  */
 export const first = <T>(
@@ -131,14 +131,14 @@ export const first = <T>(
  *
  * @param arr - An array
  * @param predicate - A predicate function.
- * @param thisArg - If provided, it will be used as the this value for each invocation of predicate. If it is not provided, `undefined` is used instead.
+ * @param thisArg - If provided, it will be used as the this value for each invocation of predicate. If it is not provided, the last element is returned.
  * @returns The last item that matches the predicate, or `None` if no item matches.
  */
 export const last = <T>(
   arr: T[],
   predicate: (value: T, index: number, array: T[]) => boolean = truePredicate,
   thisArg?: any
-): Option<T> => lastIndex(arr, predicate, thisArg).map(valueAtIndex, this);
+): Option<T> => lastIndex(arr, predicate, thisArg).map(valueAtIndex, arr);
 
 /**
  * Applies function to the elements of iterator and returns the first non-none result.