JavaScript字符串元音计数：避免常见陷阱与正确实现

const myString = "Testing for vowels";
const vowels = ["a", "e", "i", "o", "u", "y"];

function countVowelsIncorrect(myString) {
  let count = 0;
  // 错误：这里尝试检查整个 myString 是否在 vowels 数组中
  if (vowels.includes(myString)) {
    count++;
  }
  return count;
}

const resultIncorrect = countVowelsIncorrect(myString);
console.log(resultIncorrect); // 输出: 0

const myString = "Testing for vowels";
const vowels = ["a", "e", "i", "o", "u", "y"];

function countVowels(myString) {
  let count = 0;

  // 遍历字符串中的每一个字符
  for (let i = 0; i < myString.length; i++) {
    // 检查当前字符是否包含在元音数组中
    if (vowels.includes(myString[i])) {
      count++; // 如果是元音，则计数加一
    }
  }

  return count;
}

const result = countVowels(myString);
console.log(result); // 输出: 5 (e, i, o, o, e)

function countVowelsCaseInsensitive(myString) {
  let count = 0;
  const vowels = ["a", "e", "i", "o", "u", "y"];

  for (let i = 0; i < myString.length; i++) {
    const char = myString[i].toLowerCase(); // 转换为小写
    if (vowels.includes(char)) {
      count++;
    }
  }
  return count;
}

console.log(countVowelsCaseInsensitive("Hello World")); // 输出: 3 (e, o, o)
console.log(countVowelsCaseInsensitive("AEIOU"));       // 输出: 5

function countVowelsForOf(myString) {
  let count = 0;
  const vowels = ["a", "e", "i", "o", "u", "y"];

  for (const char of myString) { // 直接获取每个字符
    if (vowels.includes(char.toLowerCase())) { // 同样处理大小写
      count++;
    }
  }
  return count;
}

console.log(countVowelsForOf("Programming is Fun")); // 输出: 5 (o, a, i, i, u)

function countVowelsWithRegex(myString) {
  // 正则表达式：[aeiouy] 匹配任何一个元音
  // g 标志表示全局匹配（查找所有匹配项，而不是找到第一个就停止）
  // i 标志表示不区分大小写匹配
  const matches = myString.match(/[aeiouy]/gi);
  return matches ? matches.length : 0; // 如果没有匹配项，match() 返回 null
}

console.log(countVowelsWithRegex("Hello JavaScript")); // 输出: 5 (e, o, a, a, i)
console.log(countVowelsWithRegex("Rhythm"));           // 输出: 1 (y)