Calculate distance from user given a lattitde and longitude

gistfile1.js

/* global App:false */

'use strict';

var Lib = Lib || {};

Lib.DistanceView = Backbone.View.extend({

    latitude: 0,

    longitude: 0,

    initialize: function(){
        this.latitude = this.$el.data('lat');
        this.longitude = this.$el.data('long');
        _.bindAll(this, 'render', 'gotCoordinates');

        if(navigator.geolocation){
            navigator.geolocation.getCurrentPosition(this.gotCoordinates, this.failedToGetCoordinates);
        }
    },

    gotCoordinates: function(position){
        this.updateDistance(this.calculateDistance(this.latitude, this.longitude, position.coords.latitude, position.coords.longitude, 'K'));
    },

    calculateDistance: function(lat1, lon1, lat2, lon2, unit){
        var theta = lon1 - lon2;
        var dist = Math.sin(this.deg2rad(lat1)) * Math.sin(this.deg2rad(lat2)) +  Math.cos(this.deg2rad(lat1)) * Math.cos(this.deg2rad(lat2)) * Math.cos(this.deg2rad(theta));
        dist = Math.acos(dist);
        dist = this.rad2deg(dist);
        var miles = dist * 60 * 1.1515;
        unit = unit.toUpperCase();

        if (unit === 'K') {
            return Math.round((miles * 1.609344) * 100) / 100;
        } else if (unit === 'N') {
            return (miles * 0.8684);
        } else {
            return miles;
        }
    },

    updateDistance: function(distance){
        this.$el.find('.distance-in-km').html(distance);
    },

    failedToGetCoordinates: function(error){
        if(error.code === 1){
            console.log('Geolocation Access Denied');
        }
    },

    deg2rad: function(deg){
        return deg * (Math.PI / 180);
    },

    rad2deg: function(rad){
        return rad * (180 / Math.PI);
    }

});