How to convert JSON array to CSV using Node.js?

Question

I want to convert json which has value array. response.json

{
\"rows\": [
[
  \"New Visitor\",
  \"(not set)\",
  \"(not set)\",      
  \"0\"
]         


        

Answer 1

Three easy steps: Read. Convert. Write.

Step 1: Read.

If you need to read the JSON from a file (as indicated by your inclusion of the filename response.json in your post), you will require the Node.js FileSystem API:

const fs = require('fs');                          // Require Node.js FileSystem API.
const JSONFile = fs.readFileSync('response.json'); // Read the file synchronously.

Note: If you prefer, you can read the file asynchronously with fs.readFile() and perform the conversion in a callback function.

Step 2: Convert.

Whether you read your JSON from a local file or GET it from a server, you will need to parse it into a Plain Old JavaScript Object first using the JSON.parse method:

const JSONasPOJO = JSON.parse(JSONFile); // Parse JSON into POJO.

Then perform a series of joins on the child arrays and parent array:
SEE EDIT BELOW

/* THIS IS UNNECESSARY FOR "COMMA" SEPARATED VALUES
const CSVString = JSONasPOJO
    .rows                    // Get `rows`, which is an array.
    .map(                    // Map returns a new array.
        row => row.join(',') // Each child array becomes a comma-separated string.  
     )                    
    .join('\n');             // Parent array becomes a newline-separated string...
                             // ...of comma-separated strings.
                             // It is now a single CSV string!
*/

EDIT:

While the previous code certainly works, it is unnecessary to use .map and .join on the child arrays. As @Relu demonstrates, a single .join on the parent array is sufficient because JavaScript will automatically convert the child arrays into comma-separated strings by default since .join must return a string and cannot contain any child arrays.

You could use the above pattern if you want to join the child arrays with something other than a comma.

Otherwise:

var CSVString = JSONasPOJO.rows.join('\n'); // Array becomes a newline-separated...
                                            // ...string of comma-separated strings.
                                            // It is now a single CSV string!

Here, we can see that conversion in action:

const JSONasPOJO = {
  "rows": [
    [
      "New Visitor",
      "(not set)",
      "(not set)",      
      "0"
    ],
    [
      "New Visitor",
      "(not set)",
      "(not set)",
      "mobile"      
    ],
    [
      "New Visitor",
      "(not set)",
      "(not set)",
      "mobile"    
    ],
    [
      "New Visitor",
      "(not set)",
      "(not set)",
      "mobile" // NOTE: Here I removed a trailing comma,
               // ...which is invalid JSON!
    ]
  ]
}

const CSVString = JSONasPOJO.rows.join('\n');

console.log(CSVString);

Step 3: Write.

Using the FileSystem API again, write to a file, and log an error or a success message:

fs.writeFile('name.csv', CSVString, err => {
    if (err) return console.log(err);
    console.log('FILE SUCCESSFULLY WRITTEN!\n');
});

Note: Here, I demonstrate the asynchronous pattern using a callback to log my error and success messages. If you prefer, you can write the file synchronously with fs.writeFileSync().

Putting it all together

I like to add plenty of console.log() messages to my Node.js scripts.

const fs = require('fs');

const inFilename  = 'response.json',
      outFilename = 'name.csv';

console.log(`Preparing to read from ${inFilename} …`);

const JSONContents = fs.readFileSync(inFilename);

console.log(`READ:\n${JSONContents}`);
console.log('Preparing to parse as JSON …');

const JSONasPOJO = JSON.parse(JSONContents);

console.log(`PARSED:\n${JSONasPOJO}`);
console.log('Preparing to convert into CSV …');

const CSVString = JSONasPOJO.rows.join('\n');

console.log(`CONVERTED:\n${CSVString}`);
console.log(`Preparing to write to ${outFilename} …`);

fs.writeFile(outFilename, CSVString, err => {
    if (err) return console.error(err);
    console.log('FILE SUCCESSFULLY WRITTEN!');
});