Add case utilities

packages/utils/src/string/case.ts

@@ -0,0 +1,39 @@
+/**
+ * Lowercase the first character of a string, leaving the remainder unchanged.
+ *
+ * - Returns the input unchanged when it's an empty string
+ * - Non-alphabetic first characters are returned as-is
+ *
+ * @param str - The input string
+ * @returns The string with the first character lowercased
+ * @example
+ * lowercaseFirstChar('Hello') // 'hello'
+ * lowercaseFirstChar('hello') // 'hello'
+ * lowercaseFirstChar('1World') // '1World'
+ */
+export function lowercaseFirstChar(str: string): string {
+  if (str.length === 0) {
+    return str;
+  }
+  return str.charAt(0).toLowerCase() + str.slice(1);
+}
+
+/**
+ * Uppercase the first character of a string, leaving the remainder unchanged.
+ *
+ * - Returns the input unchanged when it's an empty string
+ * - Non-alphabetic first characters are returned as-is
+ *
+ * @param str - The input string
+ * @returns The string with the first character uppercased
+ * @example
+ * uppercaseFirstChar('hello') // 'Hello'
+ * uppercaseFirstChar('Hello') // 'Hello'
+ * uppercaseFirstChar('#tag') // '#tag'
+ */
+export function uppercaseFirstChar(str: string): string {
+  if (str.length === 0) {
+    return str;
+  }
+  return str.charAt(0).toUpperCase() + str.slice(1);
+}

packages/utils/src/string/case.unit.test.ts

@@ -0,0 +1,74 @@
+import { describe, expect, it } from 'vitest';
+
+import { lowercaseFirstChar, uppercaseFirstChar } from './case.js';
+
+describe('case utilities', () => {
+  describe('lowercaseFirstChar', () => {
+    it('lowercases the first character of a normal word', () => {
+      // Arrange
+      const input = 'HelloWorld';
+
+      // Act
+      const result = lowercaseFirstChar(input);
+
+      // Assert
+      expect(result).toBe('helloWorld');
+    });
+
+    it('returns the same string if already lowercased first char', () => {
+      const input = 'helloWorld';
+      const result = lowercaseFirstChar(input);
+      expect(result).toBe('helloWorld');
+    });
+
+    it('handles empty string', () => {
+      const input = '';
+      const result = lowercaseFirstChar(input);
+      expect(result).toBe('');
+    });
+
+    it('leaves non-alphabetic first characters unchanged', () => {
+      const input = '1World';
+      const result = lowercaseFirstChar(input);
+      expect(result).toBe('1World');
+    });
+
+    it('handles unicode characters (emoji) at start', () => {
+      const input = '😀Smile';
+      const result = lowercaseFirstChar(input);
+      expect(result).toBe('😀Smile');
+    });
+  });
+
+  describe('uppercaseFirstChar', () => {
+    it('uppercases the first character of a normal word', () => {
+      const input = 'helloWorld';
+      const result = uppercaseFirstChar(input);
+      expect(result).toBe('HelloWorld');
+    });
+
+    it('returns the same string if already uppercased first char', () => {
+      const input = 'HelloWorld';
+      const result = uppercaseFirstChar(input);
+      expect(result).toBe('HelloWorld');
+    });
+
+    it('handles empty string', () => {
+      const input = '';
+      const result = uppercaseFirstChar(input);
+      expect(result).toBe('');
+    });
+
+    it('leaves non-alphabetic first characters unchanged', () => {
+      const input = '#tag';
+      const result = uppercaseFirstChar(input);
+      expect(result).toBe('#tag');
+    });
+
+    it('handles unicode characters (emoji) at start', () => {
+      const input = '😀smile';
+      const result = uppercaseFirstChar(input);
+      expect(result).toBe('😀smile');
+    });
+  });
+});

packages/utils/src/string/index.ts

@@ -1,3 +1,4 @@
+export * from './case.js';
 export * from './convert-case-with-prefix.js';
 export * from './find-closest-match.js';
 export * from './quot.js';