判断某个点是否在圆半径内（电子围栏）

var radius = 983; //单位：米
var distance = getDistance(116.38984270516266, 39.91837578204758, 116.39904135358485, 39.91306312138842);
console.log(distance);
if (distance <= radius) {
    console.log("在圆内");
} else {
    console.log("在圆外");
}


/*计算两点之间的距离，单位：米*/
function getDistance(point1_lng, point1_lat, point2_lng, point2_lat) {
    var x1 = degreeToRad(point1_lng);
    var y1 = degreeToRad(point1_lat);
    var x2 = degreeToRad(point2_lng);
    var y2 = degreeToRad(point2_lat);
    var EARTHRADIUS = 6370996.81; //地球半径
    return (EARTHRADIUS * Math.acos(Math.sin(y1) * Math.sin(y2) + Math.cos(y1) * Math.cos(y2) * Math.cos(x2 - x1)));
}


/*将度转化为弧度*/
function degreeToRad(degree) {
    return (Math.PI * degree) / 180;
}