Copy json object with NodeJS loop into JSON file

Question

Good day,

Is there a way to make a for loop in NodeJS and copy the same json object but with different 'id' into JSON file.

Lets say that i want to add 100 objects in this format :

[ { "id": 1, "Firstname": "Sven","Secondname": "Petersen","Age": "18" }]

when the server starts.

What would be the best way to make it ? What modules should i use ?

I thought i could do something like that :

for (var i = 0; i < 500; i++) {
    fs.readFile("JSON/DB.json", "utf8", function () {
        var data = '[{ "id": 1, "Firstname": "Sven", "Secondname": "Petersen", "Age": "18", }]'
        var Data = JSON.parse(data);
        var id = i;
        for (var i = 0; i < Data; i++) {

        };

        var newData = JSON.stringify(Data);
        fs.writeFile("JSON/DB.json", newData, "utf8");
    })
};

P.S i'm a newb here

I would guess that fs is the module you are searching for when you wish to write to file. I bet googling "how to write to file nodejs" would give you a good clue on what to use ;P — Jite
– Jite, Commented Jul 26, 2016 at 10:09
Can you show us what you have attempted and where you have gone wrong. Specifically an example of your code. — alex
– alex, Commented Jul 26, 2016 at 10:21

alex · Accepted Answer · 2016-07-26 13:10:49Z

1

Edit: Convert id to string.

Try this

var fs = require('fs');

var jsonObj = '{ "id":"1","firstname": "Sven","secondname": "Petersen","age":"18" }'

var data = JSON.parse(jsonObj)
var newDataArray = []

function ObjectCreate (id, firstname, secondname, age) {
  this.id = id.toString();
  this.firstname = firstname;
  this.secondname = secondname;
  this.age = age;
}

for (var i = 1; i < 100; i++) {
  var obj = new ObjectCreate (i, data.firstname, data.secondname, data.age);
  newDataArray.push(obj);
}

var writeObject = JSON.stringify(newDataArray)

fs.writeFile('data.json', writeObject, function(err) {
  if(err) throw err;
  console.log('done');
});

edited Jul 26, 2016 at 13:10

answered Jul 26, 2016 at 12:24

alex

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5 Comments

Kirill Vorobjov Over a year ago

Thanks alot!! There is a small error with 'let' in for loop [ Block-scoped declarations <let, const, function, class> not yet supported ] so i changed it to var. Why have u used const instead of var ? And also it is somehow writes only IDs like so : [{"id":1},{"id":2},{"id":3},{"id":4}........

alex Over a year ago

You can replace all the variable declarations with var if your version of javascript does not yet support that type of variable declaration. This is habit as I am coding in ES6. You can convert the id to a string inside the object function generator.

alex Over a year ago

Made an edit to convert id to string, and to support your version of javascript.

Kirill Vorobjov Over a year ago

Thanks once again ! This programming world , i learn something new everyday :) The problem was that i've wrote var jsonObj = '[ {} ]' instead of '{ }'. Now everything works!

alex Over a year ago

I'm happy to help!

Nazar Sakharenko · Accepted Answer · 2016-07-26 13:00:30Z

1

Depend from your needs. Use streams as one of the many solutions:

const fs = require('fs');

const PATH_TO_FILE = 'path/to/file';

let data = {
  id: null,
  value: 'some value'
};

let stream = fs.createWriteStream(PATH_TO_FILE);

//error handler
stream.on('error', function (error) {

});

for(let i = 1; i < 501; i++) {
  data.id = i;
  stream.write(JSON.stringify(data));
}

stream.end();

answered Jul 26, 2016 at 13:00

Nazar Sakharenko

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2 Comments

Kirill Vorobjov Over a year ago

Thank ! Helped too !

Nazar Sakharenko Over a year ago

Np. Streams are preferable if you need write big amount of data, in other case you'd better use writeFile.

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