Saving JSON data correctly on nodeJS server - node.js

Question

I'm still working on my SPA where can I track my expenses. Each Expense Item consists of a value, a date , description and tags.
The client send all these data to my server , where I want to save it in a JSON file.
My code looks like this right now:
(json.push isnt working)
client.on('message', function(value, date, descr, tags) {
console.log('message: ' + value, date, descr, tags );
var exp = new Object();
exp.id = id;
exp.value = value;
exp.date = date;
exp.tags = tags;
expArr[exp.id] = exp;
id++;
console.log(exp.id);
fs.readFile('expenses.json', function (err, data) {
var json = JSON.parse(data);
json.push(exp);
console.log(json);
fs.writeFile("expenses.json", JSON.stringify(exp),
function(err){
if (err) throw err;
console.log('The data was appended to file!');
});
})
});
My goal is, every newly added item should append to my JSON file.
In the end it should look like this for example:
{"expArray": [{"id":0,"value":"200","date":"dqwd","tags":"cnelw"},
{"id":1,"value":"300","date":"dqwd","tags":"ncjlekw"},
{"id":2,"value":"22","date":"dqwd","tags":"dnkqoe"}
]}
I dont know if it's necessary to to do an array there?
But I need to read the file again for the future and get the ID of the items to delete them on client-side or edit them.
Thanks for ur help!

Answer 1

try this:
client.on('message', function(value, date, descr, tags) {
console.log('message: ' + value, date, descr, tags );
// exp object
var exp = {id:id,value:value,date:date,tags:tags}
expArr[exp.id] = exp;
id++;
console.log(exp.id);
fs.readFile('expenses.json', function (err, data) {
var json = JSON.parse(data);
// _------- add expArray
json.expArray.push(exp);
console.log(json);
fs.writeFile("expenses.json", JSON.stringify(exp),
function(err){
if (err) throw err;
console.log('The data was appended to file!');
});
})
});