locationServices.js

function distance(lat1, lon1, lat2, lon2, unit) {
    var radlat1 = Math.PI * lat1 / 180
    var radlat2 = Math.PI * lat2 / 180
    var theta = lon1 - lon2
    var radtheta = Math.PI * theta / 180
    var dist = Math.sin(radlat1) * Math.sin(radlat2) + Math.cos(radlat1) * Math.cos(radlat2) * Math.cos(radtheta);
    if (dist > 1) {
        dist = 1;
    }
    dist = Math.acos(dist)
    dist = dist * 180 / Math.PI
    dist = dist * 60 * 1.1515
    if (unit == "K") {
        dist = dist * 1.609344
    }
    if (unit == "N") {
        dist = dist * 0.8684
    }
    return dist.toFixed(3)
}

async function getLocation() {
    return new Promise((resolve, reject) => {
        if (Platform.OS === 'android') {
            PermissionsAndroid.request(
                PermissionsAndroid.PERMISSIONS.ACCESS_FINE_LOCATION, {
                    'title': '',
                    'message': ''
                }
            ).then(granted => {
                if (granted === PermissionsAndroid.RESULTS.GRANTED) {
                    const onSuccess = location => resolve(location.coords);
                    const onFail = error => {
                        reject(error)
                    }
                    const options = {
                        enableHighAccuracy: false,
                        timeout: 15000,
                        maximumAge: 100,
                        showLocationDialog: true
                    }
                    navigator.geolocation.getCurrentPosition(onSuccess, onFail, options)
                } else {
                    reject("App do not have location permission.")
                }
            })
        } else {
            const onSuccess = location => resolve(location.coords)
            const onFail = error => reject(error)
            const options = {
                enableHighAccuracy: true,
                timeout: 15000,
                maximumAge: 100,
                showLocationDialog: true
            }
            navigator.geolocation.getCurrentPosition(onSuccess, onFail, options)
        }
    });
}

export {
    getLocation,
    distance
};