How do I write the result from res.json to a proper json file using node.js?

Question

This is the code snippet. The query returns in json form but how do I write these values in a JSON file?

app.get('/users', function(req, res) {
    User.find({}, function(err, docs) {
        res.json(docs);

        console.error(err);
    })
});

Answer 1

If you're going to be writing to a file within a route callback handler you should use the Asynchronous writeFile() function or the fs.createWriteStream() function which are a part of the fs Module in the Node.js Core API . If not, your server will be unresponsive to any subsequent requests because the Node.js thread will be blocking while it is writing to the file system.

Here is an example usage of writeFile within your route callback handler. This code will overwrite the ./docs.json file every time the route is called.

const fs = require('fs')
const filepath = './docs.json'

app.get('/users', (req, res) => {
    Users.find({}, (err, docs) => {
      if (err)
        return res.sendStatus(500)

      fs.writeFile(filepath, JSON.stringify(docs, null, 2), err => {
        if (err)
          return res.sendStatus(500)

        return res.json(docs)
      })
    })
})

Here is an example usage of writing your JSON to a file with Streams. fs.createReadStream() is used to create a readable stream of the stringified docs object. Then that Readable is written to the filepath with a Writable stream that has the Readable data piped into it.

const fs = require('fs')

app.get('/users', (req, res) => {
    Users.find({}, (err, docs) => {
      if (err)
        return res.sendStatus(500)

      let reader = fs.createReadStream(JSON.stringify(docs, null, 2))
      let writer = fs.createWriteStream(filename)

      reader.on('error', err => {
        // an error occurred while reading
        writer.end()  // explicitly close writer
        return res.sendStatus(500)
      })

      write.on('error', err => {
        // an error occurred writing
        return res.sendStatus(500)
      })

      write.on('close', () => {
        // writer is done writing the file contents, respond to requester
        return res.json(docs)
      })

      // pipe the data from reader to writer
      reader.pipe(writer)
    })
})

Answer 2

Use node's file system library 'fs'.

const fs = require('fs');

const jsonData = { "Hello": "World" };
fs.writeFileSync('output.json', JSON.strigify(jsonData));

Docs: fs.writeFileSync(file, data[, options])