Appending JSON data to a file - json

Question

I have some data I want to write to a file periodically and I'd like to write it small JSON objects. At a later time I'd like to read them all in for processing, but the appended file of JSON objects isn't JSON itself.
So I stringify the JSON object and write them to file periodically and I get something like this;
{
"100": {
"stuff": 123
}
}
{
"300": {
"stuff": 456
}
}
{
"200": {
"stuff": 789
}
}
Of course when I try to parse the file with a simple script like the following;
var fs = require('fs');
var file = 'test.log'
var obj = JSON.parse(fs.readFileSync(file, 'utf8'));
var fs = require('fs');
var obj;
fs.readFile(file, 'utf8', function (err, data) {
if (err) throw err;
obj = JSON.parse(data);
console.log(obj);
});
...the parser freaks out because this isn't a valid JSON file, I'd need something more like;
{
"100": {
"stuff": 123
},
"300": {
"stuff": 456
},
"200": {
"stuff": 789
}
}
...but I can't get this by simply appending records. I can of course force commas between the records before writing them, but I end up missing the '{' at the start of the file, the '}' at the end of the file and would have an extra ',' on the last record. The whole things reaks of being a kludge.
I'm guessing someone has worked all of this out alreadyand there is a nice pattern for this, but I couldn't find anything from searching. Each section will have a variable amount of data so I like the flexibility JSON offers, but I don't want to store it all ahead of time before writing to disk as it will get large.
If you could point me at a good solution for this it would be appreciated.
Sincerely, Paul.

Answer 1

Why don't you use a regex before processing the object list file to add a comma. Since the pattern is a new line after every object, you could use this to find and replace: /}\n{/g.
For your sample, this should do the trick :
var fs = require('fs');
var file = 'test.log'
var obj;
fs.readFile(file, 'utf8', function (err, data) {
if (err) throw err;
var jsonString = '[' + data.replace(/}\n{/g, '},{')+ ']'; // Adding brackets in order to create an array of objects
obj = JSON.parse(jsonString);
console.log(obj);
});
Then, if you want to have an object as you specified you can use the spread operator ... to append an object to your super-object :
var fs = require('fs');
var file = 'test.log'
var obj;
fs.readFile(file, 'utf8', function (err, data) {
if (err) throw err;
var jsonString = '[' + data.replace(/}\n{/g, '},{')+ ']'; // Adding brackets in order to creat an array of objects
obj = JSON.parse(jsonString);
var superObj = {};
for (var i = 0; i < obj.length; i++) {
superObj = {...superObj,...obj[i]};
}
console.log(superObj);
});