转换为字符串时保留嵌套数组结构，JavaScript

function stringifyWithNestedArrays(obj) {
  if (Array.isArray(obj)) {
    return '[' + obj.map(stringifyWithNestedArrays).join(',') + ']';
  } else if (typeof obj === 'object' && obj !== null) {
    return '{' + Object.keys(obj).map(key => '"' + key + '":' + stringifyWithNestedArrays(obj[key])).join(',') + '}';
  } else if (typeof obj === 'string') {
    return '"' + obj + '"';
  } else {
    return String(obj);
  }
}

var obj = {
  name: 'John',
  age: 30,
  hobbies: ['reading', 'coding', ['swimming', 'running']]
};

var jsonString = stringifyWithNestedArrays(obj);
console.log(jsonString);

{
  "name":"John",
  "age":30,
  "hobbies":["reading","coding",["swimming","running"]]
}