# Calculate length of Multilinestrings/Linestrings/Polygons in geoJSON file

I have a couple of routes on my map where I would like to display the length of each route. I think I've found what I was looking for here: https://github.com/tyrasd/geojson-length, but I'm not sure how to apply the calculations.

``````<script src="js/measureLengthGeoJSON.js"></script>
``````

but then I get this error message:

``````Uncaught ReferenceError: module is not defined
at measureLengthGeoJSON.js:1
``````

Line 1 refers to: module.exports.

I then tried to copy the entire formula/function like so:

``````var lengthGeo = function(geometry) {
if (geometry.type === 'LineString')
return calculateLength(geometry.coordinates);
else if (geometry.type === 'MultiLineString')
return geometry.coordinates.reduce(function(memo, coordinates) {
return memo + calculateLength(coordinates);
}, 0);
else
return null;
}

function calculateLength(lineString) {
if (lineString.length<2)
return 0;
var result = 0;
for (var i=1; i<lineString.length; i++)
result += distance(lineString[i-1][0],lineString[i-1][1],
lineString[i  ][0],lineString[i  ][1]);
return result;
}

/**
* Calculate the approximate distance between two coordinates (lat/lon)
*
* http://www.movable-type.co.uk/scripts/latlong.html#equirectangular
*/
function distance(λ1,φ1,λ2,φ2) {
var R = 6371000;
Δλ = (λ2 - λ1) * Math.PI / 180;
φ1 = φ1 * Math.PI / 180;
φ2 = φ2 * Math.PI / 180;
var x = Δλ * Math.cos((φ1+φ2)/2);
var y = (φ2-φ1);
var d = Math.sqrt(x*x + y*y);
return R * d;
};
``````

and apply the function like so:

``````var testlength = lengthGeo(HvenKort);

console.log(testlength);
``````

Nothing is outputted to the console. I can't figure out what I'm doing wrong.

Any suggestion on how to fix it or any other library that is capable of calculation distances of Multilinestrings/Linestrings/Polygons?