feat(string): add capitalize and test case (#23)

Author: Wing-9527

src/string.test.ts

@@ -1,5 +1,5 @@
 import { expect, it } from 'vitest'
-import { ensurePrefix, ensureSuffix, slash, template } from './string'
+import { capitalize, ensurePrefix, ensureSuffix, slash, template } from './string'
 
 it('template', () => {
   expect(
@@ -49,3 +49,11 @@ it('ensureSuffix', () => {
   expect(ensureSuffix('world', 'hello ')).toEqual('hello world')
   expect(ensureSuffix('123', 'abc123')).toEqual('abc123')
 })
+
+it('capitalize', () => {
+  expect(capitalize('hello World')).toEqual('Hello world')
+  expect(capitalize('123')).toEqual('123')
+  expect(capitalize('中国')).toEqual('中国')
+  expect(capitalize('āÁĂÀ')).toEqual('Āáăà')
+  expect(capitalize('\a')).toEqual('A')
+})

src/string.ts

@@ -66,3 +66,15 @@ export function randomStr(size = 16, dict = urlAlphabet) {
     id += dict[(Math.random() * len) | 0]
   return id
 }
+
+/**
+ * First letter uppercase, other lowercase
+ * @category string
+ * @example
+ * ```
+ * capitalize('hello') => 'Hello'
+ * ```
+ */
+export function capitalize(str: string): string {
+  return str[0].toUpperCase() + str.slice(1).toLowerCase()
+}