Node.JS append JSON to array

Question

I need to append my JSON data to an array inside a JSON file. It is appending successfully. However, it does not append inside of the Brackets in the JSON file

Here is my NODE

 if (req.method == 'POST') {
    req.on('data', function (chunk) {
        fs.writeFile("comments-data.json", chunk, {'flag':'a'}, function(err) {
            if(err) {
                return console.log(err);
            }

            console.log("The file was saved!");
        })
    });
    res.end('{"msg": "success"}');
};

How can i tell it to just append inside of the brackets?

You can't just append to a JSON file and expect it to merge into the array. You need to read the file, parse the JSON to an array, push the new element onto the array, stringify the array, and then write that to the file. — Barmar
– Barmar, Commented Aug 11, 2016 at 21:46

Barmar · Accepted Answer · 2016-08-12 17:41:39Z

2

You have to parse the JSON in both the request and the file, push the requrest data onto the array, then write that back out to the file.

if (req.method == 'POST') {
    req.on('data', function(chunk) {
        var element = JSON.parse(chunk);
        fs.readFile("comments-data.json", 'r', function(err, json) {
            var array = JSON.parse(json);
            array.push(element);
            fs.writeFile("comments-data.json", JSON.stringify(array), "w", function(err) {
                if (err) {
                    console.log(err);
                    return;
                }
                console.log("The file was saved!");
            });
        });
        res.end('{"msg": "success"}');
    });
}

edited Aug 12, 2016 at 17:41

answered Aug 11, 2016 at 21:53

Barmar

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10 Comments

Grant Campbell Over a year ago

You were missing a }); at the end. Also it did not recognize 'r' so i changed it to utf8. When I try to run this snippet, I receive cannot read property push of null. @Barmar

Barmar Over a year ago

That means JSON.parse() is failing, so there's something wrong with the contents of the json file.

Grant Campbell Over a year ago

How should it be setup for the example of your snippet? I tried even a blank array.

Barmar Over a year ago

The initial contents of the file should be [].

Grant Campbell Over a year ago

Same result with the blank array

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