如何删除逗号以外的特殊字符

function removeSpecialCharacters(str) {
  let result = '';
  for (let i = 0; i < str.length; i++) {
    const char = str[i];
    if (char === ',' || /^[a-zA-Z0-9_]+$/.test(char)) {
      result += char;
    }
  }
  return result;
}

const input = 'abc,def!@#123';
const output = removeSpecialCharacters(input);
console.log(output); // 输出：abc,def123