1var fs = require('fs');
2
3var myOptions = {
4  name: 'Avian',
5  dessert: 'cake'
6  flavor: 'chocolate',
7  beverage: 'coffee'
8};
9
10var data = JSON.stringify(myOptions);
11
12fs.writeFile('./config.json', data, function (err) {
13  if (err) {
14    console.log('There has been an error saving your configuration data.');
15    console.log(err.message);
16    return;
17  }
18  console.log('Configuration saved successfully.')
19});

1const fs = require('fs');
2
3let obj = {
4    table: []
5};
6
7fs.exists('myjsonfile.json', function(exists) {
8
9    if (exists) {
10      
11        fs.readFile('myjsonfile.json', function readFileCallback(err, data) {
12
13            if (err) {
14                console.log(err);
15            } else {
16                obj = JSON.parse(data);
17
18              	//Data that you want add to the file
19                for (i = 0; i < 5; i++) {
20                    obj.table.push({
21                        id: i,
22                        square: i * i
23                    });
24                }
25
26                let json = JSON.stringify(obj);
27                fs.writeFile('myjsonfile.json', json);
28            }
29        });
30    } else {
31      
32        console.log("file not exists");
33      	
34      	//Data that you want add to the file
35        for (i = 0; i < 5; i++) {
36            obj.table.push({
37                id: i,
38                square: i * i
39            });
40        }
41
42        let json = JSON.stringify(obj);
43        fs.writeFile('myjsonfile.json', json);
44    }
45});