Turf.js code to generate buffered squares

buffer_squares.js

//define
var turf = require("turf");
var fs = require('fs');
var util = require("util");
var center = turf.point([0,0])
var distances = [10,20,30,40]

// create output container
var features = []

// create buffers
for (var i = 0; i < distances.length; i++) {
    distance = distances[i]
    buffered = turf.buffer(center,distance,"miles");e
    enveloped = turf.envelope(buffered);
    features.push(enveloped);
}

// create feature collection
fc = turf.featurecollection(features);
console.log(util.inspect(fc, false, null));

// output to file in cwd
var file = fs.createWriteStream('buffers.geojson');
file.write(JSON.stringify(fc));
file.end()