Write / add data in JSON file using Node.js Write / add data in JSON file using Node.js json json

Write / add data in JSON file using Node.js

If this JSON file won't become too big over time, you should try:

  1. Create a JavaScript object with the table array in it

    var obj = {   table: []};
  2. Add some data to it, for example:

    obj.table.push({id: 1, square:2});
  3. Convert it from an object to a string with JSON.stringify

    var json = JSON.stringify(obj);
  4. Use fs to write the file to disk

    var fs = require('fs');fs.writeFile('myjsonfile.json', json, 'utf8', callback);
  5. If you want to append it, read the JSON file and convert it back to an object

    fs.readFile('myjsonfile.json', 'utf8', function readFileCallback(err, data){    if (err){        console.log(err);    } else {    obj = JSON.parse(data); //now it an object    obj.table.push({id: 2, square:3}); //add some data    json = JSON.stringify(obj); //convert it back to json    fs.writeFile('myjsonfile.json', json, 'utf8', callback); // write it back }});

This will work for data that is up to 100 MB effectively. Over this limit, you should use a database engine.


Create a function which returns the current date (year+month+day) as a string. Create the file named this string + .json. the fs module has a function which can check for file existence named fs.stat(path, callback).With this, you can check if the file exists. If it exists, use the read function if it's not, use the create function. Use the date string as the path cuz the file will be named as the today date + .json. the callback will contain a stats object which will be null if the file does not exist.

Please try the following program. You might be expecting this output.

var fs = require('fs');var data = {}data.table = []for (i=0; i <26 ; i++){   var obj = {       id: i,       square: i * i   }   data.table.push(obj)}fs.writeFile ("input.json", JSON.stringify(data), function(err) {    if (err) throw err;    console.log('complete');    });

Save this program in a javascript file, say, square.js.

Then run the program from command prompt using the command node square.js

What it does is, simply overwriting the existing file with new set of data, every time you execute the command.

Happy Coding.

you should read the file, every time you want to add a new property to the json, and then add the the new properties

var fs = require('fs');fs.readFile('data.json',function(err,content){  if(err) throw err;  var parseJson = JSON.parse(content);  for (i=0; i <11 ; i++){   parseJson.table.push({id:i, square:i*i})  }  fs.writeFile('data.json',JSON.stringify(parseJson),function(err){    if(err) throw err;  })})