javascript - 如何将 Replacer 函数与 JSON Stringify 结合使用？

Question

我一直在尝试使用

const fs = require("fs");
const settings = require("./serversettings.json")
let reason = args.join(' ');
function replacer(key, value) {
    return reason;
}
fs.writeFileSync(settings, JSON.stringify(settings.logchannel, replacer))

在我看来，它不起作用，所以我试图弄清楚替换器是如何工作的，因为 MDN 让我更加困惑。

Answer 1

replacer 函数采用一个键和一个值(当它传递对象及其子对象时)，并预计返回一个新值(字符串类型)来替换原始值。如果返回 undefined，则结果字符串中将省略整个键值对。

示例:

1. 记录传递给替换函数的所有键值对:

var obj = {
  "a": "textA",
  "sub": {
    "b": "textB"
  }
};

var logNum = 1;
function replacer(key, value) {
  console.log("--------------------------");
  console.log("Log number: #" + logNum++);
  console.log("Key: " + key);
  console.log("Value:", value);
  
  return value;                    // return the value as it is so we won't interupt JSON.stringify
}

JSON.stringify(obj, replacer);

将字符串 "- alter" 添加到所有字符串值:

var obj = {
  "a": "textA",
  "sub": {
    "b": "textB"
  }
};

function replacer(key, value) {
  if(typeof value === "string")    // if the value of type string
    return value + " - altered";   // then append " - altered" to it
  return value;                    // otherwise leave it as it is
}

console.log(JSON.stringify(obj, replacer, 4));

省略所有数字类型的值:

var obj = {
  "a": "textA",
  "age": 15,
  "sub": {
    "b": "textB",
    "age": 25
  }
};

function replacer(key, value) {
  if(typeof value === "number")    // if the type of this value is number
    return undefined;              // then return undefined so JSON.stringify will omitt it 
  return value;                    // otherwise return the value as it is
}

console.log(JSON.stringify(obj, replacer, 4));