write/add data in JSON file using node.js

If this json file won't become too big over the time you should try:

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

   var obj = {
      table: []
   };
   

2. Add some data to it like

   obj.table.push({id: 1, square:2});
   

3. Convert it from an object to string with 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 big as 100 MB max effectively. Over this limit, you should use a database engine.

UPDATE:

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.

Above example is also correct, but i provide simple example:

var fs = require("fs");
var sampleObject = {
    name: 'pankaj',
    member: 'stack',
    type: {
        x: 11,
        y: 22
    }
};

fs.writeFile("./object.json", JSON.stringify(sampleObject, null, 4), (err) => {
    if (err) {
        console.error(err);
        return;
    };
    console.log("File has been created");
});

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;
  })
})

For formatting jsonfile gives spaces option which you can pass as a parameter:

   jsonfile.writeFile(file, obj, {spaces: 2}, function (err) {
         console.error(err);
   })

Or use jsonfile.spaces = 4. Read details here.

I would not suggest writing to file each time in the loop, instead construct the JSON object in the loop and write to file outside the loop.

var jsonfile = require('jsonfile');
var obj={
     'table':[]
    };

for (i=0; i <11 ; i++){
       obj.table.push({"id":i,"square":i*i});
}
jsonfile.writeFile('loop.json', obj, {spaces:2}, function(err){
      console.log(err);
});

try

var fs = require("fs");
var sampleObject = { your data };

fs.writeFile("./object.json", JSON.stringify(sampleObject, null, 4), (err) => {
    if (err) {  console.error(err);  return; };
    console.log("File has been created");
});

For synchronous approach

fs.writeFileSync('file.json', JSON.stringify(jsonVariable));