新增 countCharacters.js, 计算字符串中每个字符的出现次数

lib/string/countCharacters.js

@@ -0,0 +1,19 @@
+/**
+ * 计算字符串中每个字符的出现次数。
+ * @author penn <https://github.com/penn201500>
+ * @category string
+ * @alias yd_string_countCharacters
+ * @param {String} str - 字符串。
+ * @returns {Object} - 包含每个字符的出现次数的对象。
+ *
+ * @example
+ * console.log(countCharacters("hello world"))
+ * // 输出: { h: 1, e: 1, l: 3, o: 2, ' ': 1, w: 1, r: 1, d: 1 }
+ */
+export default function countCharacters(str) {
+    const count = {};
+    for (const char of str) {
+        count[char] = (count[char] || 0) + 1;
+    }
+    return count;
+}

lib/string/countCharacters.test.js

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+import { it, expect, describe } from 'vitest';
+import yd_string_countCharacters from './countCharacters.js';
+
+describe('yd_string_countCharacters', () => {
+    it('should correctly return counts for each characters in a string', () => {
+        const result = yd_string_countCharacters('hello');
+        expect(result).toEqual({ h: 1, e: 1, l: 2, o: 1 });
+    });
+
+    it('should handle a string with numbers', () => {
+        const result = yd_string_countCharacters('hello42');
+        expect(result).toEqual({ h: 1, e: 1, l: 2, o: 1, 4: 1, 2: 1 });
+    });
+
+    it('should handle a string with special characters', () => {
+        const result = yd_string_countCharacters('hello!@');
+        expect(result).toEqual({ h: 1, e: 1, l: 2, o: 1, '!': 1, '@': 1 });
+    });
+
+    it('should handle an empty string', () => {
+        const result = yd_string_countCharacters('');
+        expect(result).toEqual({});
+    });
+});