此代码有效：
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);
