Have you read http://www.w3schools.com/html/html5_geolocation.asp

What you want to do is check the errors to see if they allowed it or denied the request.

function getLocation() {
  if (navigator.geolocation) {
    navigator.geolocation.getCurrentPosition(showPosition,showError);
  } else {
    x.innerHTML = "Geolocation is not supported by this browser.";
  }
}

function showPosition(position) {
  x.innerHTML = "Latitude: " + position.coords.latitude + "<br>Longitude: " + position.coords.longitude;    
}

function showError(error) {
  switch(error.code) {
    case error.PERMISSION_DENIED:
      x.innerHTML = "User denied the request for Geolocation."
      break;
    case error.POSITION_UNAVAILABLE:
      x.innerHTML = "Location information is unavailable."
      break;
    case error.TIMEOUT:
      x.innerHTML = "The request to get user location timed out."
      break;
    case error.UNKNOWN_ERROR:
      x.innerHTML = "An unknown error occurred."
      break;
  }
}

You would need to set a cookie with a value and basically check to see if the cookie exists if it doesnt then you can "detect location"

If the user does not allow your app to use the Geolocation API the methods getCurrentPosition and watchPosition will return an PositionError object via the error callback:

void getCurrentPosition(successCallback,
                        errorCallback,
                        options);

long watchPosition(successCallback,
                   errorCallback,
                   options);

The PositionError looks like:

PositionError {
    code;
    message;
};

where the possibles values of code are:

PositionError.PERMISSION_DENIED = 1;
PositionError.POSITION_UNAVAILABLE = 2;
PositionError.TIMEOUT = 3;

And more specific:

• PERMISSION_DENIED (numeric value 1) The location acquisition process failed because the document does not have permission to use the Geolocation API.

The documentation here.

watchPosition and getCurrentPosition both accept a second callback which is invoked when there is an error. The error callback provides an argument for an error object. For permission denied, error.code would be error.PERMISSION_DENIED (numeric value 1).

Read more here: https://developer.mozilla.org/en/Using_geolocation

Example:

Copynavigator.geolocation.watchPosition(function(position) {
    console.log("i'm tracking you!");
  },
  function(error) {
    if (error.code == error.PERMISSION_DENIED)
      console.log("you denied me :-(");
  });

EDIT: As @Ian Devlin pointed out, it doesn't seem Firefox (4.0.1 at the time of this post) supports this behavior. It works as expected in Chrome and probably Safari etc.

Try Modernizr.

You can initialise with the tests you need, of which Geolocation is one of them.

As per the docs you can try something like this:

Modernizr.load({
    test: Modernizr.geolocation,
    yep : 'geo.js',
    nope: 'geo-polyfill.js'
});

Where in this example it tests for geolocation and then selectively loads a javascript file depending on the result.

It will also add a .geolocation class to the body DOM element if the device supports it, so you can simply test to see whether this class exists in order to determine if geolocation is supported / enabled.

Thanks to @GabrielePetrioli's comment. The code below uses navigator.permissions.queryPermissions Status Change Event

I am checking if permission was granted and updating the application by calling the function which updates location.

const [locationAccess, setLocationAccess] = useState(false);//user changes in browser
...
      //check user location changes in navigator
      navigator.permissions.query({ name: 'geolocation' }).then((permissionStatus) => {
       
          permissionStatus.onchange = () => {
          setLocationAccess(permissionStatus.state=="granted")

          if (permissionStatus.state=="granted") {
              attemptLocation();
            }
          };
        });

  

It isn't possible with the geolocation API but it is possible with the new permission API

This code is useful if you want to try to receive the coordinates but don't want to bother the user with a prompt dialog cuz the coordinates is not that important and may as well fallback to geoIP

function getCoords() {
  return new Promise((resolve, reject) =>
    navigator.permissions ?

      // Permission API is implemented
      navigator.permissions.query({
        name: 'geolocation'
      }).then(permission =>
        // is geolocation granted?
        permission.state === "granted"
          ? navigator.geolocation.getCurrentPosition(pos => resolve(pos.coords)) 
          : resolve(null)
      ) :

    // Permission API was not implemented
    reject(new Error("Permission API is not supported"))
  )
}

getCoords().then(coords => console.log(coords))

This will resolve to null if permission hasn't been granted, cast a error if some javascript code wasn't supported by the browser and resolve to the coordinates if it has been granted