refactor: improves performance isContainNil in the first and last index

Author: Kevin Hermawan

README.md

@@ -92,7 +92,7 @@ console.log(result3); // true
 >
 > O(n), where n is the length of the array.
 >
-> O(1), if `index` is the last index of the array.
+> O(1), if nil appears in the first or last index.
 
 #### [isEmpty](/src/isEmpty.ts)
 

src/isContainNil.ts

@@ -1,13 +1,17 @@
 export function isContainNil<T>(array: T[]) {
-  let result = false;
-
-  for (let i = 0; i < array.length; i++) {
-    if (array[i] === undefined || array[i] === null) {
-      result = true;
+  if (
+    array.length > 0 &&
+    (array[0] === null ||
+      array[0] === undefined ||
+      array[array.length - 1] === null ||
+      array[array.length - 1] === undefined)
+  ) {
+    return true;
+  }
 
-      break;
-    }
+  for (let i = 1; i < array.length - 1; i++) {
+    if (array[i] === null || array[i] === undefined) return true;
   }
 
-  return result;
+  return false;
 }

test/isContainNil.test.ts

@@ -4,20 +4,30 @@ import { isContainNil } from '../src/isContainNil';
 
 describe('isContainNil', () => {
   it('tests with array that contains `undefined`', () => {
-    const array = [1, 2, 3, undefined, 5];
+    const array1 = [undefined, 2, 3, 4, 5];
+    const array2 = [1, 2, undefined, 4, 5];
+    const array3 = [1, 2, 3, 4, undefined];
 
-    const result = isContainNil(array);
-    expect(result).to.eql(true);
+    const result1 = isContainNil(array1);
+    const result2 = isContainNil(array2);
+    const result3 = isContainNil(array3);
+
+    expect([result1, result2, result3]).to.eql([true, true, true]);
   });
 
   it('tests with array that contains `undefined`', () => {
-    const array = [1, 2, 3, null, 5];
+    const array1 = [null, 2, 3, 4, 5];
+    const array2 = [1, 2, null, 4, 5];
+    const array3 = [1, 2, 3, 4, null];
 
-    const result = isContainNil(array);
-    expect(result).to.eql(true);
+    const result1 = isContainNil(array1);
+    const result2 = isContainNil(array2);
+    const result3 = isContainNil(array3);
+
+    expect([result1, result2, result3]).to.eql([true, true, true]);
   });
 
-  it('tests with clean array', () => {
+  it('tests with clear array', () => {
     const array = [1, 2, 3, 4, 5];
 
     const result = isContainNil(array);