How Do I Use The Replacer Function With JSON Stringify?

问题

I've been trying to use

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))

It seems like to me that it doesn't work, so I'm trying to figure out how replacers work as MDN made me even more confused.

回答1:

The replacer function takes a key and a value (as it passes through the object and its sub objects) and is expected to return a new value (of type string) that will replace the original value. If undefined is returned then the whole key-value pair is omitted in the resulting string.

Examples:

Log all key-value pairs passed to the replacer function:

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);

Add the string " - altered" to all string values:

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));

Omitt all values of type number:

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));

回答2:

settings is an object, not a filename.

I'm trying to replace the string in the settings named as "logchannel" to whatever I tell it to change it to

const fs = require("fs");
var settings = require("./serversettings.json");
settings.logchannel = "foo"; //specify value of logchannel here
fs.writeFileSync("./serversettings.json", JSON.stringify(settings));

来源：https://stackoverflow.com/questions/46873496/how-do-i-use-the-replacer-function-with-json-stringify

标签

javascript

json

node.js