add: 00014-easy-first

00014-easy-first.ts

@@ -0,0 +1,22 @@
+// ============= Test Cases =============
+import type { Equal, Expect } from './test-utils';
+
+type cases = [Expect<Equal<First<[3, 2, 1]>, 3>>, Expect<Equal<First<[() => 123, { a: string }]>, () => 123>>, Expect<Equal<First<[]>, never>>, Expect<Equal<First<[undefined]>, undefined>>];
+
+type errors = [
+  // @ts-expect-error
+  First<'notArray'>,
+  // @ts-expect-error
+  First<{ 0: 'arrayLike' }>
+];
+
+// ============= Your Code Here =============
+
+// 判断是否为空数组
+// type First<T extends any[]> = T extends [] ? never : T[0];
+
+// 判断长度是否为 0
+// type First<T extends any[]> = T['length'] extends 0 ? never : T[0];
+
+// 使用 infer 取第零个元素
+type First<T extends any[]> = T extends [infer F, ...any[]] ? F : never;