(譯)JSON.STRINGIFY替換參數的功能

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

我有一個有趣的問題讓我有些困惑。下面讓我分享我所學到的知識，也許當您遇到相似挑戰時能夠節省您一些時間。讓咱們一塊兒享受JSON.stringify的樂趣吧~

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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沒有驚喜。不幸的是，個人項目（AWS DynamoDB 好奇野獸）中使用的架構迫使我不得不處理ES6zhong的Set。所以事情變得更有趣。看看這個：

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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我覺得Set值將被轉換爲一個普通數組。您可能已經猜到我錯了, Sets，WeakSets，Maps和WeakMaps被忽略或替換爲null。不過仍是有但願的——JSON.stringify可選的第二個參數容許咱們處理全部Sets並將它們轉換爲數組。

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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問題解決了👏

（TIL）Today I Learned

JSON.stringify()接受第二個可選參數，該參數能夠是遞歸替換器函數或者是白名單鍵的數組。像這樣：

// 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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第三個參數能夠是string或number。它決定要用做分隔符的文本或空格的數量。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，請保持好奇💋