Calculate the distance between two points on the earth based on the longitude and latitude. js implementation code

Using JS to calculate the distance between two points on the earth based on latitude and longitude
Recently, we used the formula for calculating the distance between two points on the earth's surface based on latitude and longitude, and then implemented it using JS.
There are two ways to calculate the distance between two points on the Earth's surface.

FirstBy default, The Earth is a smooth sphere, and The Distance between any two points is calculated. This Distance is called The Great Circle Distance ).
The formula is as follows:
Use JS to achieve:Copy codeCode: var EARTH_RADIUS = 6378137.0; // unit: M
Var PI = Math. PI;

Function getRad (d ){
Return d * PI/180.0;
}

/**
* Caculate the great circle distance
* @ Param {Object} lat1
* @ Param {Object} lng1
* @ Param {Object} lat2
* @ Param {Object} lng2
*/
Function getGreatCircleDistance (lat1, lng1, lat2, lng2 ){
Var radLat1 = getRad (lat1 );
Var radLat2 = getRad (lat2 );

Var a = radLat1-radLat2;
Var B = getRad (lng1)-getRad (lng2 );

Var s = 2 * Math. asin (Math. sqrt (Math. pow (Math. sin (a/2), 2) + Math. cos (radLat1) * Math. cos (radLat2) * Math. pow (Math. sin (B/2), 2 )));
S = s * EARTH_RADIUS;
S = Math. round (s * 10000)/10000.0;

Return s;
}

This formula is correct in most cases. problems may occur only when dealing with relative points on the sphere,There is a formula for correction.Because there is no need, you can find it on the wiki.
Of course, we all know that the earth is not a real sphere, but an elliptical sphere, so we have the following formula:Copy codeThe Code is as follows :/**
* Approx distance between two points on earth ellipsoid
* @ Param {Object} lat1
* @ Param {Object} lng1
* @ Param {Object} lat2
* @ Param {Object} lng2
*/
Function getFlatternDistance (lat1, lng1, lat2, lng2 ){
Var f = getRad (lat1 + lat2)/2 );
Var g = getRad (lat1-lat2)/2 );
Var l = getRad (lng1-lng2)/2 );

Var sg = Math. sin (g );
Var sl = Math. sin (l );
Var sf = Math. sin (f );

Var s, c, w, r, d, h1, h2;
Var a = EARTH_RADIUS;
Var fl = 1/298. 257;

Sg = sg * sg;
Sl = sl * sl;
Sf = sf * sf;

S = sg * (1-sl) + (1-sf) * sl;
C = (1-sg) * (1-sl) + sf * sl;

W = Math. atan (Math. sqrt (s/c ));
R = Math. sqrt (s * c)/w;
D = 2 * w *;
H1 = (3 * r-1)/2/c;
H2 = (3 * r + 1)/2/s;

Return d * (1 + fl * (h1 * sf * (1-sg)-h2 * (1-sf) * sg ));
}

The result calculated by this formula is better than the first one. Of course, the longitude of the final result depends on the accuracy of the Input coordinates.