load coordinate data from a GPX file

loadGpx.js

// load coordinate data from a GPX file
// the input will be a file uploaded by user
// the output will be a list of coordinates
function loadGPXFile(file) {
    var reader = new FileReader();
    reader.onload = function(e) {
        var xml = e.target.result;
        var gpx = new window.DOMParser().parseFromString(xml, "text/xml");
        var coordinates = [];
        var tracks = gpx.getElementsByTagName("trk");
        for (var i = 0; i < tracks.length; i++) {
            var segments = tracks[i].getElementsByTagName("trkseg");
            for (var j = 0; j < segments.length; j++) {
                var points = segments[j].getElementsByTagName("trkpt");
                for (var k = 0; k < points.length; k++) {
                    var lat = parseFloat(points[k].getAttribute("lat"));
                    var lon = parseFloat(points[k].getAttribute("lon"));
                    coordinates.push([lat, lon]);
                }
            }
        }
        console.log(coordinates);
    }
    reader.readAsText(file);
}