js正则匹配字符出现的次数

function countChar(str, char) {
    // 创建一个正则表达式，用于匹配目标字符
    const regex = new RegExp(char, 'g');
    // 使用match方法找到所有匹配项，如果没有匹配项则返回null
    const matches = str.match(regex);
    // 如果matches为null，则返回0；否则返回匹配项的数量
    return matches ? matches.length : 0;
}

// 示例用法
const text = "JavaScript is a powerful language.";
const charToCount = 'a';
console.log(`The character '${charToCount}' appears ${countChar(text, charToCount)} times.`);

function escapeRegExp(string) {
    return string.replace(/[.*+?^${}()|[\]\\]/g, '\\$&'); // $&表示整个匹配的子串
}

const specialChar = '.';
const escapedChar = escapeRegExp(specialChar);
console.log(`The character '${escapedChar}' appears ${countChar(text, escapedChar)} times.`);