(译)JSON.STRINGIFY替换参数的功能

原文：TIL — THE POWER OF JSON.STRINGIFY REPLACER PARAMETER

我有一个有趣的问题让我有些困惑。下面让我分享我所学到的知识，也许当您遇到相似挑战时能够节省您一些时间。让咱们一块儿享受JSON.stringify的乐趣吧~

const dude = {
  name: "Pawel",
  friends: ["Dan", "Pedro", "Mr Gregory"]
};
const dudeStringified = JSON.stringify(dude);

console.log(dudeStringified);
// {"name":"Pawel","friends":["Dan","Pedro","Mr Gregory"]}
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没有惊喜。不幸的是，个人项目（AWS DynamoDB 好奇野兽）中使用的架构迫使我不得不处理ES6zhong的Set。所以事情变得更有趣。看看这个：

const dude = {
  name: "Pawel",
  friends: new Set(["Dan", "Pedro", "Mr Gregory"])
};
const dudeStringified = JSON.stringify(dude);

console.log(dudeStringified);
// {"name":"Pawel","friends":{}}
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我觉得Set值将被转换为一个普通数组。您可能已经猜到我错了, Sets，WeakSets，Maps和WeakMaps被忽略或替换为null。不过仍是有但愿的——JSON.stringify可选的第二个参数容许咱们处理全部Sets并将它们转换为数组。

const dude = {
  name: "Pawel",
  friends: new Set(["Dan", "Pedro", "Mr Gregory"])
};
const dudeStringified = JSON.stringify(dude, (key, value) =>
  value instanceof Set ? [...value] : value
);

console.log(dudeStringified);
// {"name":"Pawel","friends":["Dan","Pedro","Mr Gregory"]}
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问题解决了👏

（TIL）Today I Learned

JSON.stringify()接受第二个可选参数，该参数能够是递归替换器函数或者是白名单键的数组。像这样：

// Second argument as a replacer function

const dude = {
  name: "Dan"
};
const dudeStringified = JSON.stringify(dude, (key, value) =>
  key === "name" ? "Pawel" : value
);

console.log(dudeStringified);
// {"name":"Pawel"}
// Second argument as an array of white-listed keywords

const dude = {
  name: "Pawel",
  friends: new Set(["Dan", "Pedro", "Mr Gregory"])
};

const dudeStringified = JSON.stringify(dude, ["name"]);

console.log(dudeStringified);
// {"name":"Pawel"}
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第三个参数能够是string或number。它决定要用做分隔符的文本或空格的数量。看下面：

// Third argument as a number

const dude = {
  name: "Pawel",
  friends: ["Dan", "Pedro", "Mr Gregory"]
};
const dudeStringified = JSON.stringify(dude, null, 4);

console.log(dudeStringified);
// {
// "name": "Pawel",
// "friends": [
// "Dan",
// "Pedro",
// "Mr Gregory"
// ]
// }
// Third argument as a string

const dude = {
  name: "Pawel",
  friends: ["Dan", "Pedro", "Mr Gregory"]
};
const dudeStringified = JSON.stringify(dude, null, "🍆");

console.log(dudeStringified);
// {
// 🍆"name": "Pawel",
// 🍆"friends": [
// 🍆🍆"Dan",
// 🍆🍆"Pedro",
// 🍆🍆"Mr Gregory"
// 🍆]
// }
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直到下次，请保持好奇💋