how to push a data with key of an array of objects without overwriting existing json data using node js?

Question

I have an object that looks like this:

{
  "mark": [
    {
     "id":1,
    "name": "mark",
      "age":26
    },
    {
       "id":2,
     "name": "mark",
      "age":25
    }
],
"jack": [
    {
        "id":1,
      "name": "jack",
      "age":26
     
    },
    {
        "id":2,
      "name": "jack",
      "age": 24,
      
    }
  ]
}

WHAT I GOT AS OUTPUT IF A NEW USER IS ADDED IT IS NOT APPENDED, BUT IT IS OVERWRITTEN OR CREATED AS A NEW OBJECT

{
     "mark": [
            {
             "id":1,
            "name": "mark",
              "age":26
            },
            {
               "id":2,
             "name": "mark",
              "age":25
            }
        ],
        "jack": [
            {
                "id":1,
              "name": "jack",
              "age":26
             
            },
            {
                "id":2,
              "name": "jack",
              "age": 24,
              
            }
          ],
 
        }   "Josh": [ 
            {
                "id":1,
              "name": "Josh",
              "age":26
             
            },
            {
                "id":2,
              "name": "Josh",
              "age": 24,
              
            }
          ]

Expected

if new person data arrives in my JSON File, that should be appended to the next array with key values of array of Objects,

like

     {
          "mark": [
            {
             "id":1,
            "name": "mark",
              "age":26
            },
            {
               "id":2,
             "name": "mark",
              "age":25
            }
        ],
        "jack": [
            {
                "id":1,
              "name": "jack",
              "age":26
             
            },
            {
                "id":2,
              "name": "jack",
              "age": 24,
              
            }
          ],
"Josh": [ 
            {
                "id":1,
              "name": "Josh",
              "age":26
             
            },
            {
                "id":2,
              "name": "Josh",
              "age": 24,
              
            }
          ]
        }

I've tried this method after reading the JSON file

var newObject = array.reduce(function (obj, value) {
  var key = `${value.name}`;
  if (obj[key] == null) obj[key] = [];

  obj[key].push(value);
  return obj;
}, {});

console.log(newObject);

fs.appendFile("users.json", newObject, (err) => {
  res.send(JSON.stringify(newObject));
});

Answer 1

Like the advice already given, but using async fs i/o.

import { promises as fs } from 'fs';  // or require('fs').promises

// inside the OP's route
  const filename = 'users.json';
  try {
    const array = await fs.readFile(filename);

    // OP's code here
    // const newObject = array.reduce(...

    await fs.writeFile(filename, newObject);
    return res.send(JSON.stringify(newObject));

  } catch (error) {
    return res.status(500).send({ message: 'error' });
  }

Also note that all this is what a database does.

Answer 2

You have to first read the data from the JSON and append the new object to the JSON data and then write it back to the file.

const data = fs.readFileSync('users.json');
.
.
fs.writeFileSync('users.json', {...data, ...newObject});