Take a geojson feature as file and returns its circumference/length

getLineDistance.js

var fs = require('fs');
var turf = require('turf');

fs.readFile('feature.geojson', 'utf8', function (err,data) {
  if (err) {
    return console.log(err);
  }
  var feature = JSON.parse(data);
  var length = turf.lineDistance(feature);
  console.log(length + 'km');
});