add keys to a json file, remove duplicates and write to json file in javascript

Question

I want to add data from another Json file to another without overwriting the existing one. I just can't get any further, the console always gives me the following:

Console output 
Data 
string  
[
    "follow1",
    "follow2",
    "follow3",
    "follow4",
    "[\"follow5\",\"follow6\",\"follow7\",\"follow8\",\"follow9\"]"
]

This is my code, I would like to add the data but without square brackets and without backslashes. It would be really nice if someone could help me. Thanks very much

const user = require('./user.json');
const oldUser = user.user_follwos["user1"];
const data = require('./data.json');
const toAdd = JSON.stringify(data);

const result = JSON.stringify(toAdd);
oldUser.push(...toAdd.split(' '))
const newData = JSON.stringify(oldUser, null, 4)
console.log('\nData \n' + typeof newData + '  \n' + newData);

and here are my json files

//user.json
{
  "application_id": "123546789",
  "user_follwos": {
    "user1": [
      "follow1",
      "follow2",
      "follow3",
      "follow4"
    ],
    "user2": [
      "followA",
      "followB",
      "followC",
      "followD"
    ]
  },
 ...
 ...
}

//data.json
[
  "follow5",
  "follow6",
  "follow7",
  "follow8",
  "follow9"
]

Answer 1

First of all to do something you need both data in json

• Make 2 arrays
• Remove duplicates
• Then push data without duplicates.

Put everything together

let allTogether = data.push(...oldUser);

Create unique array

uniq = [...new Set(allTogether )];

Finally set this unique data to specific key

user_follwos.user1 = uniq

Hope this is what you need

Update with example

    let user = {
    "application_id": "123546789",
    "user_follwos": {
    "user1": [
      "follow1",
      "follow2",
      "follow3",
      "follow4"
    ],
    "user2": [
      "followA",
      "followB",
      "followC",
      "followD"
    ]
  }
};

let data = [
  "follow5",
  "follow6",
  "follow7",
  "follow8",
  "follow9"
];

let oldUser = user["user_follwos"]["user1"];
console.log(`This is old user array`);
console.log(oldUser);
let allTogether = [];
allTogether.push(...data)
allTogether.push(...oldUser);
console.log(`After we put all together`);
console.log(allTogether);
uniq = [...new Set(allTogether )];
console.log(`Getting unique values`);
console.log(uniq);
oldUser = uniq;
console.log(`Now olds user is`);
console.log(oldUser);