如何检查当前经度/经度是否在给定经度/经度20公里内

function calculateDistance(lat1, lon1, lat2, lon2) {
  const R = 6371; // 地球半径，单位为千米
  const dLat = (lat2 - lat1) * Math.PI / 180;
  const dLon = (lon2 - lon1) * Math.PI / 180;
  const a =
    Math.sin(dLat / 2) * Math.sin(dLat / 2) +
    Math.cos(lat1 * Math.PI / 180) * Math.cos(lat2 * Math.PI / 180) *
    Math.sin(dLon / 2) * Math.sin(dLon / 2);
  const c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1 - a));
  const distance = R * c; // 距离，单位为千米
  return distance;
}

function checkWithinRange(currentLat, currentLon, targetLat, targetLon) {
  const distance = calculateDistance(currentLat, currentLon, targetLat, targetLon);
  return distance <= 20;
}

// 示例使用
const currentLat = 39.9087; // 当前位置的纬度
const currentLon = 116.3975; // 当前位置的经度
const targetLat = 39.9075; // 给定位置的纬度
const targetLon = 116.3970; // 给定位置的经度

const isWithinRange = checkWithinRange(currentLat, currentLon, targetLat, targetLon);
console.log(`当前位置是否在给定位置的20公里范围内：${isWithinRange}`);