Append text to existing json file node.js

Question

I'm trying to add a new text to an existing json file, I tried writeFileSync and appendFileSync however the text added doesn't format as json even when i use JSON.stringify.

const fs = require('fs');

fs.readFile("test.json", (err, data) => {
  if( err) throw err;

  var data = JSON.parse(data);
  console.log(data);
});

var student = {
  age: "23"
};

fs.appendFileSync("test.json", "age: 23");
// var writeData = fs.writeFileSync("test.json", JSON.stringify(student));

My json file

{ name: "kevin" }

Append turns out like this, {name: "kevin"}age: "23" and writeFileSync turns out like {name: "kevin"}{age: "23"}

What I want is to continuously add text to my json file like so

{
  name: "kevin",
  age: "23"
}

Answer 1

First, dont use readFileSync and writeFileSync. They block the execution, and go against node.js standards. Here is the correct code:

const fs = require('fs');

fs.readFile("test.json", (err, data) => {  // READ
    if (err) {
        return console.error(err);
    };

    var data = JSON.parse(data.toString());
    data.age = "23"; // MODIFY
    var writeData = fs.writeFile("test.json", JSON.stringify(data), (err, result) => {  // WRITE
        if (err) {
            return console.error(err);
        } else {
            console.log(result);
            console.log("Success");
        }

    });
});

What this code does:

1. Reads the data from the file.
2. Modifies the data to get the new data the file should have.
3. Write the data(NOT append) back to the file.

Answer 2

Here's what you can do: read the data from the file, edit that data, then write it back again.

const fs = require("fs")

fs.readFile("test.json", (err, buffer) => {
  if (err) return console.error('File read error: ', err)

  const data = JSON.parse(buffer.toString())

  data.age = 23

  fs.writeFile("test.json", JSON.stringify(data), err => {
    if (err) return console.error('File write error:', err)
  })
})