function addSpanTags(jsonString) {
  let obj = JSON.parse(jsonString);

  function process(obj) {
    if (Array.isArray(obj)) {
      for (let i = 0; i < obj.length; i++) {
        obj[i] = process(obj[i]);
      }
    } else if (typeof obj === 'object' && obj !== null) {
      for (let key in obj) {
        if (obj.hasOwnProperty(key)) {
          obj[key] = process(obj[key]);
        }
      }
    } else if (typeof obj === 'string') {
      // 在这里添加span标签
      obj = `<span>${obj}</span>`;
    }

    return obj;
  }

  obj = process(obj);

  return JSON.stringify(obj);
}

const jsonString = '{"name": "John", "age": 30, "city": "New York"}';
const result = addSpanTags(jsonString);
console.log(result);