feat(compat): implement upperFirst/lowerFirst

benchmarks/performance/lowerFirst.bench.ts

@@ -1,8 +1,10 @@
 import { bench, describe } from 'vitest';
 import { lowerFirst as lowerFirstToolkit_ } from 'es-toolkit';
+import { lowerFirst as lowerFirstCompatToolkit_ } from 'es-toolkit/compat';
 import { lowerFirst as lowerFirstLodash_ } from 'lodash';
 
 const lowerFirstToolkit = lowerFirstToolkit_;
+const lowerFirstCompatToolkit = lowerFirstCompatToolkit_;
 const lowerFirstLodash = lowerFirstLodash_;
 
 describe('lowerFirst', () => {
@@ -12,6 +14,11 @@ describe('lowerFirst', () => {
       lowerFirstToolkit(str);
     });
 
+    bench('es-toolkit/compat/lowerFirst', () => {
+      const str = 'camelCase';
+      lowerFirstCompatToolkit(str);
+    });
+
     bench('lodash/lowerFirst', () => {
       const str = 'camelCase';
       lowerFirstLodash(str);
@@ -24,6 +31,10 @@ describe('lowerFirst', () => {
       lowerFirstToolkit(LONG_STR);
     });
 
+    bench('es-toolkit/compat/lowerFirst', () => {
+      lowerFirstCompatToolkit(LONG_STR);
+    });
+
     bench('lodash/lowerFirst', () => {
       lowerFirstLodash(LONG_STR);
     });

benchmarks/performance/upperFirst.bench.ts

@@ -1,8 +1,10 @@
 import { bench, describe } from 'vitest';
 import { upperFirst as upperFirstToolkit_ } from 'es-toolkit';
+import { upperFirst as upperFirstCompatToolkit_ } from 'es-toolkit/compat';
 import { upperFirst as upperFirstLodash_ } from 'lodash';
 
 const upperFirstToolkit = upperFirstToolkit_;
+const upperFirstCompatToolkit = upperFirstCompatToolkit_;
 const upperFirstLodash = upperFirstLodash_;
 
 describe('upperFirst', () => {
@@ -12,6 +14,11 @@ describe('upperFirst', () => {
       upperFirstToolkit(str);
     });
 
+    bench('es-toolkit/compat/upperFirst', () => {
+      const str = 'camelCase';
+      upperFirstCompatToolkit(str);
+    });
+
     bench('lodash/upperFirst', () => {
       const str = 'camelCase';
       upperFirstLodash(str);
@@ -24,6 +31,10 @@ describe('upperFirst', () => {
       upperFirstToolkit(LONG_STR);
     });
 
+    bench('es-toolkit/compat/upperFirst', () => {
+      upperFirstCompatToolkit(LONG_STR);
+    });
+
     bench('lodash/upperFirst', () => {
       upperFirstLodash(LONG_STR);
     });

src/compat/index.ts

@@ -167,6 +167,7 @@ export { endsWith } from './string/endsWith.ts';
 export { escape } from './string/escape.ts';
 export { kebabCase } from './string/kebabCase.ts';
 export { lowerCase } from './string/lowerCase.ts';
+export { lowerFirst } from './string/lowerFirst.ts';
 export { pad } from './string/pad.ts';
 export { padEnd } from './string/padEnd.ts';
 export { padStart } from './string/padStart.ts';
@@ -181,6 +182,7 @@ export { trim } from './string/trim.ts';
 export { trimEnd } from './string/trimEnd.ts';
 export { trimStart } from './string/trimStart.ts';
 export { upperCase } from './string/upperCase.ts';
+export { upperFirst } from './string/upperFirst.ts';
 export { words } from './string/words.ts';
 
 export { constant } from './util/constant.ts';

src/compat/string/lowerFirst.spec.ts

@@ -0,0 +1,22 @@
+import { describe, expect, it } from 'vitest';
+import { lowerFirst } from './lowerFirst';
+import { map } from '../array/map';
+import { stubString } from '../util/stubString';
+
+describe('lowerFirst', () => {
+  it('should lowercase only the first character', () => {
+    expect(lowerFirst('fred')).toBe('fred');
+    expect(lowerFirst('Fred')).toBe('fred');
+    expect(lowerFirst('FRED')).toBe('fRED');
+  });
+
+  it('should return an empty string for empty values', () => {
+    // eslint-disable-next-line no-sparse-arrays
+    const values = [, null, undefined, ''];
+    const expected = map(values, stubString);
+
+    const actual = map(values, (value, index) => (index ? lowerFirst(value as any) : lowerFirst()));
+
+    expect(actual).toEqual(expected);
+  });
+});

src/compat/string/lowerFirst.ts

@@ -0,0 +1,17 @@
+import { lowerFirst as lowerFirstToolkit } from '../../string/lowerFirst.ts';
+import { toString } from '../util/toString.ts';
+
+/**
+ * Converts the first character of string to lower case.
+ *
+ * @param {string} str - The string that is to be changed
+ * @returns {string} - The converted string.
+ *
+ * @example
+ * const convertedStr1 = lowerCase('fred') // returns 'fred'
+ * const convertedStr2 = lowerCase('Fred') // returns 'fred'
+ * const convertedStr3 = lowerCase('FRED') // returns 'fRED'
+ */
+export function lowerFirst(str?: string): string {
+  return lowerFirstToolkit(toString(str));
+}

src/compat/string/upperFirst.spec.ts

@@ -0,0 +1,22 @@
+import { describe, expect, it } from 'vitest';
+import { upperFirst } from './upperFirst';
+import { map } from '../array/map';
+import { stubString } from '../util/stubString';
+
+describe('upperFirst', () => {
+  it('should uppercase only the first character', () => {
+    expect(upperFirst('fred')).toBe('Fred');
+    expect(upperFirst('Fred')).toBe('Fred');
+    expect(upperFirst('FRED')).toBe('FRED');
+  });
+
+  it('should return an empty string for empty values', () => {
+    // eslint-disable-next-line no-sparse-arrays
+    const values = [, null, undefined, ''];
+    const expected = map(values, stubString);
+
+    const actual = map(values, (value, index) => (index ? upperFirst(value as any) : upperFirst()));
+
+    expect(actual).toEqual(expected);
+  });
+});

src/compat/string/upperFirst.ts

@@ -0,0 +1,17 @@
+import { upperFirst as upperFirstToolkit } from '../../string/upperFirst.ts';
+import { toString } from '../util/toString.ts';
+
+/**
+ * Converts the first character of string to upper case.
+ *
+ * @param {string} str - The string that is to be changed
+ * @returns {string} - The converted string.
+ *
+ * @example
+ * const convertedStr1 = upperFirst('fred') // returns 'Fred'
+ * const convertedStr2 = upperFirst('Fred') // returns 'Fred'
+ * const convertedStr3 = upperFirst('FRED') // returns 'FRED'
+ */
+export function upperFirst(str?: string): string {
+  return upperFirstToolkit(toString(str));
+}