Using the Haversine Formula in Javascript
Why not try the straight forward solution? Instead of extending Number prototype, just define toRad as a regular function:
function toRad(x) {
return x * Math.PI / 180;
}
and then call toRad
everywhere:
var dLat = toRad(lat2-lat1);
Extending the Number prototype does not always work as expected. For example calling 123.toRad() does not work. I think that if you do var x1 = lat2 - lat1; x1.toRad();
works better than doing (lat2-lat1).toRad()
Here's a refactored function based on 3 of the other answers!
Please note that the coords arguments are [longitude, latitude].
function haversineDistance(coords1, coords2, isMiles) {
function toRad(x) {
return x * Math.PI / 180;
}
var lon1 = coords1[0];
var lat1 = coords1[1];
var lon2 = coords2[0];
var lat2 = coords2[1];
var R = 6371; // km
var x1 = lat2 - lat1;
var dLat = toRad(x1);
var x2 = lon2 - lon1;
var dLon = toRad(x2)
var a = Math.sin(dLat / 2) * Math.sin(dLat / 2) +
Math.cos(toRad(lat1)) * Math.cos(toRad(lat2)) *
Math.sin(dLon / 2) * Math.sin(dLon / 2);
var c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1 - a));
var d = R * c;
if(isMiles) d /= 1.60934;
return d;
}
ES6 JavaScript/NodeJS refactored version:
/**
* Calculates the haversine distance between point A, and B.
* @param {number[]} latlngA [lat, lng] point A
* @param {number[]} latlngB [lat, lng] point B
* @param {boolean} isMiles If we are using miles, else km.
*/
const haversineDistance = ([lat1, lon1], [lat2, lon2], isMiles = false) => {
const toRadian = angle => (Math.PI / 180) * angle;
const distance = (a, b) => (Math.PI / 180) * (a - b);
const RADIUS_OF_EARTH_IN_KM = 6371;
const dLat = distance(lat2, lat1);
const dLon = distance(lon2, lon1);
lat1 = toRadian(lat1);
lat2 = toRadian(lat2);
// Haversine Formula
const a =
Math.pow(Math.sin(dLat / 2), 2) +
Math.pow(Math.sin(dLon / 2), 2) * Math.cos(lat1) * Math.cos(lat2);
const c = 2 * Math.asin(Math.sqrt(a));
let finalDistance = RADIUS_OF_EARTH_IN_KM * c;
if (isMiles) {
finalDistance /= 1.60934;
}
return finalDistance;
};
See codepen for tests against accepted answer: https://codepen.io/harrymt/pen/dyYvLpJ?editors=1011
This code is working:
Number.prototype.toRad = function() {
return this * Math.PI / 180;
}
var lat2 = 42.741;
var lon2 = -71.3161;
var lat1 = 42.806911;
var lon1 = -71.290611;
var R = 6371; // km
//has a problem with the .toRad() method below.
var x1 = lat2-lat1;
var dLat = x1.toRad();
var x2 = lon2-lon1;
var dLon = x2.toRad();
var a = Math.sin(dLat/2) * Math.sin(dLat/2) +
Math.cos(lat1.toRad()) * Math.cos(lat2.toRad()) *
Math.sin(dLon/2) * Math.sin(dLon/2);
var c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1-a));
var d = R * c;
alert(d);
Notice how I defined x1 and x2. Play with it at: https://tinker.io/3f794