Append javascript object to json file

Question

I'm returning a javascript object and I'm trying to append it to a json file using fs.appendFile. When I test the output of the file at, json formatter website, I get the error Multiple JSON root elements. Can someone please show me what I'm doing wrong here.

var data = {
  userProfile: {
    name: "Eric"
  },
  purchases: [
    {
      title: "book name"
    },
    {
      title: "book name two"
    }
  ]
};

fs.appendFile("data.json", JSON.stringify(data, null, 2), function(err) {
  if (err) {
    console.log("There was an error writing the backup json file.", err);
  }
  console.log("The backup json file has been written.");
});

I believe this question is a duplicate of https://stackoverflow.com/questions/36093042/how-do-i-add-to-an-existing-json-file-in-node-js — BoyePanthera
– BoyePanthera, Commented Dec 20, 2019 at 2:42

ittus · Accepted Answer · 2019-12-20 02:32:31Z

3

You neede to open your file, parse the JSON, append your new data to the old data, transform it back into a string and save it again.

var fs = require('fs')

var newData = {
  userProfile: {
    name: "Eric"
  },
  purchases: [
    {
      title: "book name"
    },
    {
      title: "book name two"
    }
  ]
};

fs.readFile('data.json', function (err, data) {
    var json = JSON.parse(data)
    const newJSON = Object.assign(json, newData)
    fs.writeFile("data.json", JSON.stringify(newJSON))
})

answered Dec 20, 2019 at 2:32

ittus

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5 Comments

bp123 Over a year ago

For some reason, this code doesn't append the new data. It seems to overnight the old data with the new data.

bp123 Over a year ago

The same as newData

ittus Over a year ago

You can't have two sample key (for example userProfile in 1 JSON). Is your root object an array or just an object?

bp123 Over a year ago

It's an object. Should it be an array?

ittus Over a year ago

It depends on your purpose. It you want a list of users, then it should be an array. Then const newJSON = json.push(newData) instead.

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