如何将包含货币信息的Object列表转换为指定键值对Object？

这是个很常见的数据结构转换需求，我给你分享几种JavaScript下的实现方式，都是针对你给出的JSON数组场景：

1. 现代JS首选：Array.reduce() #

这是最简洁且常用的写法，利用数组的reduce方法逐步构建目标对象：

const currencyArray = [ {"id":1,"name":"USD - US Dollar","country":"US","created_at":"2018-05-28 14:54:24","updated_at":"2018-05-28 14:54:24"}, {"id":2,"name":"TH- Thai Bat","country":"TH","created_at":"2018-05-28 14:54:24","updated_at":"2018-05-28 14:54:24"} ];

const mappedCurrency = currencyArray.reduce((acc, currentItem) => {
  acc[currentItem.country] = currentItem.name;
  return acc;
}, {});

console.log(mappedCurrency);
// 输出：{"US": "USD - US Dollar","TH": "TH- Thai Bat"}

逻辑说明：reduce的第一个参数是回调函数，acc是我们要构建的空对象（第二个参数{}是初始值），每次遍历数组元素时，把当前元素的country作为键、name作为值存入acc，最后返回这个累加后的对象。

2. 兼容性友好：传统for循环 #

如果需要兼容较老的浏览器环境，传统循环写法更稳妥：

const currencyArray = [ {"id":1,"name":"USD - US Dollar","country":"US","created_at":"2018-05-28 14:54:24","updated_at":"2018-05-28 14:54:24"}, {"id":2,"name":"TH- Thai Bat","country":"TH","created_at":"2018-05-28 14:54:24","updated_at":"2018-05-28 14:54:24"} ];

const mappedCurrency = {};
for (let i = 0; i < currencyArray.length; i++) {
  const item = currencyArray[i];
  mappedCurrency[item.country] = item.name;
}

console.log(mappedCurrency);
// 同样得到目标结果

逻辑说明：先初始化空对象，然后遍历数组的每一项，直接给对象赋值对应的键值对，逻辑直观，没有API兼容性问题。

3. ES2019+简洁写法：Object.fromEntries() #

如果你的运行环境支持ES2019及以上，这种写法会更优雅：

const currencyArray = [ {"id":1,"name":"USD - US Dollar","country":"US","created_at":"2018-05-28 14:54:24","updated_at":"2018-05-28 14:54:24"}, {"id":2,"name":"TH- Thai Bat","country":"TH","created_at":"2018-05-28 14:54:24","updated_at":"2018-05-28 14:54:24"} ];

const mappedCurrency = Object.fromEntries(
  currencyArray.map(item => [item.country, item.name])
);

console.log(mappedCurrency);

逻辑说明：先用map把原数组转换成[键, 值]格式的二维数组，再通过Object.fromEntries直接将二维数组转换为目标对象，代码非常简洁。

注意事项 #

如果原数组中存在多个相同country的元素，后面元素的name会覆盖前面的，这个是所有方案的共同特性，需要根据你的业务场景提前处理重复数据。

内容的提问来源于stack exchange，提问作者tree em