Calculate distance in km from longitude e latitude of google maps

Ionic Framework ionic-v3
8

Maybe this functions can help to get an approach. You should translate them into TypeScript, or ES6.

function degToRad(n)
{
	return n * Math.PI / 180;
}

function radToDeg(n)
{
	return n * 180 / Math.PI;
}

function getDistance(lat1, lon1, lat2, lon2, mode)
{	
	var R = 6371; // Earth radius in km
	
	switch(mode)
	{	
		case 'spherical':
		default:
			var dLon = degToRad(lon2 - lon1);
			lat1 = degToRad(lat1);
			lat2 = degToRad(lat2);
			var d = Math.acos(Math.sin(lat1) * Math.sin(lat2) + Math.cos(lat1) * Math.cos(lat2) * Math.cos(dLon)) * R;
		break;	
		
		case 'haversine':
			var dLat = degToRad(lat2 - lat1);
			var dLon = degToRad(lon2 - lon1);
			lat1 = degToRad(lat1);
			lat2 = degToRad(lat2);
			var a = Math.sin(dLat / 2) * Math.sin(dLat / 2) + Math.sin(dLon / 2) * Math.sin(dLon / 2) * Math.cos(lat1) * Math.cos(lat2); 
			var c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1 - a)); 
			var d = R * c;
		break;	
		
		case 'rectangle':
			var x = degToRad(lon2 - lon1) * Math.cos(degToRad(lat1 + lat2) / 2);
			var y = degToRad(lat2 - lat1);
			var d = Math.sqrt(x * x + y * y) * R;
		break;	
	}
		
	return d;	
}
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