如何用JavaScript将多维对象Reduce为指定格式的字符串

给定对象：

obj = {
      "zozo": {
          "buys": "6",
          "sells": "9"
      },
      "zaza": {
          "buys": "5",
          "sells": "2"
      }
}

需要将其转换为字符串：zozo: buys(6) sells(9), zaza: buys(5) sells(2)

现有代码：

obj = {
      "zozo": {
          "buys": "6",
          "sells": "9"
      },
      "zaza": {
          "buys": "5",
          "sells": "2"
      }
}
      
res = Object.entries(obj).reduce((x,y) => `${x}, ${y[0]}: buys(${y[1].buys}) sells(${y[1].sells})`, '');
console.log(res);

输出结果为：, zozo: buys(6) sells(9), zaza: buys(5) sells(2)，开头多了一个逗号，原因是传入空字符串作为reduce的初始值，导致第一次拼接时会在空字符串后加逗号和第一个元素。

解决方案 #

方法1：使用map() + join()（推荐） #

这种方法逻辑更直观，先将每个键值对转换成目标格式的字符串，再用, 连接所有结果，完全避免多余前缀：

const obj = {
  "zozo": {
      "buys": "6",
      "sells": "9"
  },
  "zaza": {
      "buys": "5",
      "sells": "2"
  }
};

const res = Object.entries(obj)
  .map(([name, data]) => `${name}: buys(${data.buys}) sells(${data.sells})`)
  .join(', ');

console.log(res); // 输出：zozo: buys(6) sells(9), zaza: buys(5) sells(2)

方法2：修正reduce()的用法 #

通过判断当前元素的索引，避免第一个元素前添加逗号：

const obj = {
  "zozo": {
      "buys": "6",
      "sells": "9"
  },
  "zaza": {
      "buys": "5",
      "sells": "2"
  }
};

const res = Object.entries(obj).reduce((acc, [name, data], index) => {
  const itemStr = `${name}: buys(${data.buys}) sells(${data.sells})`;
  return index === 0 ? itemStr : `${acc}, ${itemStr}`;
}, '');

console.log(res);

方法3：拆分第一个元素再拼接 #

适合需要处理空对象的场景，先取出第一个元素作为初始值，再循环拼接后续元素：

const obj = {
  "zozo": {
      "buys": "6",
      "sells": "9"
  },
  "zaza": {
      "buys": "5",
      "sells": "2"
  }
};

const entries = Object.entries(obj);
let res = '';

if (entries.length > 0) {
  const [firstName, firstData] = entries[0];
  res = `${firstName}: buys(${firstData.buys}) sells(${firstData.sells})`;
  
  for (let i = 1; i < entries.length; i++) {
    const [name, data] = entries[i];
    res += `, ${name}: buys(${data.buys}) sells(${data.sells})`;
  }
}

console.log(res);

内容的提问来源于stack exchange，提问作者vulpinus