Simple Node.js program which accepts a string of JSON array, make it flat and returns as a string in stdout

flatten.js

#!/usr/bin/env node

'use strict';

// Program accepts only json array string on stdin
// You need node.js with version >= v6.2.2
// Examples of usage:
//
// $ echo "[1,2,[3,4],[5,[6],7],8]" | node flatten.js
// [1,2,3,4,5,6,7,8]
//
// $ echo "[1, [2,3], [4,[5,[6]]]]" | node flatten.js
// [1,2,3,4,5,6]
//
// $ echo "{data: "wrong input" }" | node flatten.js
// Not a valid JSON array format!
// Example: 'echo "[1,2,[3],4]" | node flatten.js'
//
var stdin = process.stdin,
    stdout = process.stdout,
    stderr = process.stderr,
    data = [];


var flatten = function flatten(arr) {
  return arr.reduce(function (a, b) {
    return a.concat(Array.isArray(b) ? flatten(b) : b);
  }, []);
};

stdin.resume();
stdin.setEncoding('utf8');

stdin.on('data', function (chunk) {
    data.push(chunk);
});

stdin.on('end', function () {
    var inputJSON = data.join(),
        parsedData,
        output;

    try {
        parsedData = JSON.parse(inputJSON);
        if (!Array.isArray(parsedData)) {
            throw 'not an array'
        }
    } catch(e) {
        stderr.write('Not a valid JSON array format!\n');
        stderr.write('Example: \'echo "[1,2,[3],4]" | node flatten.js\'\n');
        process.exit(1)
    }

    output = JSON.stringify(flatten(parsedData), null, '')
    stdout.write(output)
    stderr.write('\n');
    process.exit()
});