Failed to append data in .json file using node

Question

I want to append my data which is array of object format to the existing .json file so I have written code for it, but on stackoverflow I noticed so many developers suggesting before appending to existing json file first read file and then push new data to existing json file. So I followed this and made changes according to this but getting error :

TypeError [ERR_INVALID_CALLBACK]: Callback must be a function. Received undefined

Code written in node

 newdata=[
  {
    UserId: '11',
    UserName: 'harry',
   
  },
  {
    UserId: 12,
    UserName: 'David',
  }
];

     fs.readFile('results.json', function (err, data) {
    if(data === '') {
        json = JSON.parse(newdata);
        json.push(newdata);
    }
    fs.writeFile("results.json", JSON.stringify(json));
  })

fs.writeFile needs as third/last option a function/callback: RTFM: nodejs.org/dist/latest-v16.x/docs/api/… — Marc
– Marc, Commented Jan 19, 2022 at 11:30

Helio Albano · Accepted Answer · 2022-01-19 11:30:38Z

2

This error is because you are using the .writeFile in a wrong way.

Try something like this:

fs.writeFile('results.json', JSON.stringify(newData), function(err) {
    if (err) throw err; 
});

A short explanation:

The ERR_INVALID_CALLBACK in the error message is the missing of the function informed in the last parameter in the example above.

fs.writeFile(<file>, <content>, <callback>)

answered Jan 19, 2022 at 11:30

Helio Albano

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