feat: add isFirst and isLast methods

Author: brielov

README.md

@@ -125,13 +125,13 @@ function TodoList() {
             <button onClick={() => removeTodo(index)}>Delete</button>
             <button
               onClick={() => moveTodo(index, 'up')}
-              disabled={index === 0}
+              disabled={todos.isFirst(index)}
             >
               ↑
             </button>
             <button
               onClick={() => moveTodo(index, 'down')}
-              disabled={index === todos.size - 1}
+              disabled={todos.isLast(index)}
             >
               ↓
             </button>

src/index.ts

@@ -139,6 +139,38 @@ export class List<T> implements Iterable<T> {
     return resolved < 0 || resolved >= this.size
   }
 
+  /**
+   * Checks if the given index corresponds to the first element in the List.
+   * Does not resolve negative indices.
+   *
+   * @example
+   * ```ts
+   * const list = List.of(1, 2, 3);
+   * list.isFirst(0); // true
+   * list.isFirst(1); // false
+   * list.isFirst(-1); // false
+   * ```
+   */
+  isFirst(index: number): boolean {
+    return !this.isEmpty() && index === 0
+  }
+
+  /**
+   * Checks if the given index corresponds to the last element in the List.
+   * Does not resolve negative indices.
+   *
+   * @example
+   * ```ts
+   * const list = List.of(1, 2, 3);
+   * list.isLast(2); // true
+   * list.isLast(1); // false
+   * list.isLast(-1); // false
+   * ```
+   */
+  isLast(index: number): boolean {
+    return index === this.size - 1
+  }
+
   /**
    * Appends items to the end of the List.
    *

tests/index.test.ts

@@ -248,6 +248,44 @@ describe('List', () => {
       })
     })
 
+    describe('isFirst', () => {
+      it('should return true for index 0', () => {
+        const list = List.of(1, 2, 3)
+        expect(list.isFirst(0)).toBe(true)
+      })
+
+      it('should return false for other indices', () => {
+        const list = List.of(1, 2, 3)
+        expect(list.isFirst(1)).toBe(false)
+        expect(list.isFirst(2)).toBe(false)
+        expect(list.isFirst(-1)).toBe(false)
+      })
+
+      it('should handle empty list', () => {
+        const list = List.empty()
+        expect(list.isFirst(0)).toBe(false)
+      })
+    })
+
+    describe('isLast', () => {
+      it('should return true for last index', () => {
+        const list = List.of(1, 2, 3)
+        expect(list.isLast(2)).toBe(true)
+      })
+
+      it('should return false for other indices', () => {
+        const list = List.of(1, 2, 3)
+        expect(list.isLast(0)).toBe(false)
+        expect(list.isLast(1)).toBe(false)
+        expect(list.isLast(-1)).toBe(false)
+      })
+
+      it('should handle empty list', () => {
+        const list = List.empty()
+        expect(list.isLast(0)).toBe(false)
+      })
+    })
+
     describe('difference', () => {
       it('should return items in first list but not in second', () => {
         const list1 = List.of(1, 2, 3, 4)