feat(toLower): Implement toLower

docs/ja/reference/compat/string/toLower.md

@@ -0,0 +1,36 @@
+# toLower
+
+::: info
+この関数は互換性のために `es-toolkit/compat` からのみインポートできます。代替可能なネイティブ JavaScript API があるか、まだ十分に最適化されていないためです。
+
+`es-toolkit/compat` からこの関数をインポートすると、[lodash と完全に同じように動作](../../../compatibility.md)します。
+:::
+
+与えられた値を文字列に変換し、小文字に変換します。与えられた入力は最初に文字列に変換されます。
+
+## インターフェース
+
+```typescript
+function toLower(value?: unknown): string;
+```
+
+### パラメータ
+
+- `value` (`unknown`): 変換する値。
+
+### 戻り値
+
+(`string`): 小文字に変換された文字列を返します。
+
+## 例
+
+```typescript
+toLower('--FOO-BAR--');
+// => '--foo-bar--'
+
+toLower(null);
+// => ''
+
+toLower([1, 2, 3]);
+// => '1,2,3'
+```

docs/ko/reference/compat/string/toLower.md

@@ -0,0 +1,36 @@
+# toLower
+
+::: info
+이 함수는 호환성을 위한 `es-toolkit/compat` 에서만 가져올 수 있어요. 대체할 수 있는 네이티브 JavaScript API가 있거나, 아직 충분히 최적화되지 않았기 때문이에요.
+
+`es-toolkit/compat`에서 이 함수를 가져오면, [lodash와 완전히 똑같이 동작](../../../compatibility.md)해요.
+:::
+
+주어진 값을 문자열로 변환하고 소문자로 변환해요. 주어진 인자는 먼저 문자열로 변환돼서 처리돼요.
+
+## 인터페이스
+
+```typescript
+function toLower(value?: unknown): string;
+```
+
+### 파라미터
+
+- `value` (`unknown`): 변환할 값.
+
+### 반환 값
+
+(`string`): 소문자로 변환된 문자열.
+
+## 예시
+
+```typescript
+toLower('--FOO-BAR--');
+// => '--foo-bar--'
+
+toLower(null);
+// => ''
+
+toLower([1, 2, 3]);
+// => '1,2,3'
+```

docs/reference/compat/string/toLower.md

@@ -0,0 +1,36 @@
+# toLower
+
+::: info
+This function is only available in `es-toolkit/compat` for compatibility reasons. It either has alternative native JavaScript APIs or isn’t fully optimized yet.
+
+When imported from `es-toolkit/compat`, it behaves exactly like lodash and provides the same functionalities, as detailed [here](../../../compatibility.md).
+:::
+
+Converts the given value to a string and transforms it to lower case. The function can handle various input types by first converting them to strings.
+
+## Signature
+
+```typescript
+function toLower(value?: unknown): string;
+```
+
+### Parameters
+
+- `value` (`unknown`): The value to convert.
+
+### Returns
+
+(`string`): Returns the lower cased string.
+
+## Examples
+
+```typescript
+toLower('--FOO-BAR--');
+// => '--foo-bar--'
+
+toLower(null);
+// => ''
+
+toLower([1, 2, 3]);
+// => '1,2,3'
+```

docs/reference/compat/string/toUpper.md

@@ -6,7 +6,7 @@ This function is only available in `es-toolkit/compat` for compatibility reasons
 When imported from `es-toolkit/compat`, it behaves exactly like lodash and provides the same functionalities, as detailed [here](../../../compatibility.md).
 :::
 
-Converts the given value to a string and transforms it to uppercase. The function can handle various input types by first converting them to strings.
+Converts the given value to a string and transforms it to upper case. The function can handle various input types by first converting them to strings.
 
 ## Signature
 
@@ -16,11 +16,11 @@ function toUpper(value?: unknown): string;
 
 ## Parameters
 
-- `value`(`unknown`) : The value to convert to uppercase. If omitted, returns an empty string.
+- `value`(`unknown`) : The value to convert to upper case. If omitted, returns an empty string.
 
 ## Returns
 
-`string` : The uppercase version of the input value converted to a string.
+`string` : The upper case version of the input value converted to a string.
 
 ## Examples
 

docs/zh_hans/reference/compat/string/toLower.md

@@ -0,0 +1,36 @@
+# toLower
+
+::: info
+出于兼容性原因，此函数仅在 `es-toolkit/compat` 中提供。它可能具有替代的原生 JavaScript API，或者尚未完全优化。
+
+从 `es-toolkit/compat` 导入时，它的行为与 lodash 完全一致，并提供相同的功能，详情请见 [这里](../../../compatibility.md)。
+:::
+
+将给定的值转换为字符串并转换为小写。给定的输入首先会被转换为字符串。
+
+## 签名
+
+```typescript
+function toLower(value?: unknown): string;
+```
+
+### 参数
+
+- `value` (`unknown`): 要转换的值。
+
+### 返回值
+
+(`string`): 返回小写的字符串.
+
+## 示例
+
+```typescript
+toLower('--FOO-BAR--');
+// => '--foo-bar--'
+
+toLower(null);
+// => ''
+
+toLower([1, 2, 3]);
+// => '1,2,3'
+```

src/compat/index.ts

@@ -176,6 +176,7 @@ export { snakeCase } from './string/snakeCase.ts';
 export { startCase } from './string/startCase.ts';
 export { startsWith } from './string/startsWith.ts';
 export { template, templateSettings } from './string/template.ts';
+export { toLower } from './string/toLower.ts';
 export { toUpper } from './string/toUpper.ts';
 export { trim } from './string/trim.ts';
 export { trimEnd } from './string/trimEnd.ts';

src/compat/string/toLower.spec.ts

@@ -0,0 +1,116 @@
+import { describe, expect, it } from 'vitest';
+import { toLower } from './toLower';
+
+describe('toLower', () => {
+  it('should convert whole string to lower case', () => {
+    expect(toLower('--Foo-Bar--')).toEqual('--foo-bar--');
+    expect(toLower('fooBar')).toEqual('foobar');
+    expect(toLower('__FOO_BAR__')).toEqual('__foo_bar__');
+  });
+
+  const strings = ['foo bar', 'Foo bar', 'foo Bar', 'Foo Bar', 'FOO BAR', 'fooBar', '--foo-bar--', '__foo_bar__'];
+
+  it('should convert string to upper case while preserving special characters', () => {
+    const actual = strings.map(string => toLower(string));
+    const expected = ['foo bar', 'foo bar', 'foo bar', 'foo bar', 'foo bar', 'foobar', '--foo-bar--', '__foo_bar__'];
+    expect(actual).toEqual(expected);
+  });
+
+  it('should handle double-converting strings', () => {
+    const actual = strings.map(string => toLower(toLower(string)));
+    const expected = strings.map(string => toLower(string));
+    expect(actual).toEqual(expected);
+  });
+
+  it('should preserve contractions with apostrophes', () => {
+    const postfixes = ['d', 'll', 'm', 're', 's', 't', 've'];
+    ["'", '\u2019'].forEach(apos => {
+      const actual = postfixes.map(postfix => toLower(`a b${apos}${postfix} c`));
+      const expected = postfixes.map(postfix => `A B${apos}${postfix.toLowerCase()} C`);
+      expect(actual).toEqual(expected);
+    });
+  });
+
+  it('should preserve spaces and special characters', () => {
+    expect(toLower('hello   world')).toBe('HELLO   WORLD');
+    expect(toLower('!@#$hello%^&*')).toBe('!@#$HELLO%^&*');
+    expect(toLower('tabs\tand\nnewlines')).toBe('TABS\tAND\nNEWLINES');
+  });
+
+  it('should handle unicode characters', () => {
+    expect(toLower('café')).toBe('CAFÉ');
+    expect(toLower('über')).toBe('ÜBER');
+    expect(toLower('señor')).toBe('SEÑOR');
+  });
+
+  it('should preserve Latin mathematical operators', () => {
+    expect(toLower('\xd7')).toBe('\xd7');
+    expect(toLower('\xf7')).toBe('\xf7');
+  });
+
+  it('should handle null and undefined', () => {
+    expect(toLower(null)).toBe('');
+    expect(toLower(undefined)).toBe('');
+  });
+
+  it('should handle numbers including special cases', () => {
+    expect(toLower(123)).toBe('123');
+    expect(toLower(-0)).toBe('-0');
+    expect(toLower(0)).toBe('0');
+    expect(toLower(Infinity)).toBe('INFINITY');
+    expect(toLower(NaN)).toBe('NAN');
+  });
+
+  it('should handle arrays', () => {
+    expect(toLower([1, 2, 3])).toBe('1,2,3');
+    expect(toLower(['a', 'b', 'c'])).toBe('A,B,C');
+    expect(toLower([1, 'b', -0])).toBe('1,B,-0');
+    expect(toLower([])).toBe('');
+  });
+
+  it('should handle nested arrays', () => {
+    expect(toLower([1, [2, 3], 4])).toBe('1,2,3,4');
+    expect(toLower([[['a']]])).toBe('A');
+  });
+
+  it('should handle symbols', () => {
+    const sym1 = Symbol('test');
+    const sym2 = Symbol('');
+    expect(toLower(sym1)).toBe('SYMBOL(TEST)');
+    expect(toLower(sym2)).toBe('SYMBOL()');
+    expect(toLower([Symbol('a'), Symbol('b')])).toBe('SYMBOL(A),SYMBOL(B)');
+  });
+
+  it('should handle objects', () => {
+    const obj = { toString: () => 'custom' };
+    expect(toLower(obj)).toBe('CUSTOM');
+    expect(toLower({})).toBe('[OBJECT OBJECT]');
+  });
+
+  it('should handle mixed types in arrays', () => {
+    const sym = Symbol('test');
+    expect(toLower([1, 'b', sym, null, undefined])).toBe('1,B,SYMBOL(TEST),,');
+  });
+
+  it('should maintain proper TypeScript types', () => {
+    const result1: string = toLower('test');
+    const result2: string = toLower(123);
+    const result3: string = toLower(null);
+    const result4: string = toLower(undefined);
+
+    expect(typeof result1).toBe('string');
+    expect(typeof result2).toBe('string');
+    expect(typeof result3).toBe('string');
+    expect(typeof result4).toBe('string');
+  });
+
+  it('should handle empty strings', () => {
+    expect(toLower('')).toBe('');
+  });
+
+  it('should handle whitespace strings', () => {
+    expect(toLower(' ')).toBe(' ');
+    expect(toLower('\t')).toBe('\t');
+    expect(toLower('\n')).toBe('\n');
+  });
+});

src/compat/string/toLower.ts

@@ -0,0 +1,22 @@
+import { toString } from '../util/toString.ts';
+
+/**
+ * Converts the given value to a string and transforms it to lower case.
+ * The function can handle various input types by first converting them to strings.
+ *
+ * @param {unknown} [value=''] The value to convert.
+ * @returns {string} Returns the lower cased string.
+ * @example
+ *
+ * toLower('--FOO-BAR--');
+ * // => '--foo-bar--'
+ *
+ * toLower(null);
+ * // => ''
+ *
+ * toLower([1, 2, 3]);
+ * // => '1,2,3'
+ */
+export function toLower(value?: unknown): string {
+  return toString(value).toLowerCase();
+}