Question

I am trying to write a function that returns an object representing the position of the device: I have tried:

  function getDevicePosition () {
    var positionObject;
    if (isDeviceReady) {
        navigator.geolocation.getCurrentPosition(function (position) {

            positionObject = position;
            console.log('location updated');
            console.log(positionObject.coords.longitude);//1. works
        }, function (err) {
            console.log('Failed to get device position' + err);
            return null;
        });

    } else {
        warnUser();
        return null;
    }
    console.log(positionObject.coords.longitude);//2. doesnt work as positionObject is null.
    return positionObject;
}

Notice that I have added comments marking statement 1 and statement 2. If I initialized position object in statement 1. Why is it undefined in statement 2?

Answer 1

Because getCurrentPosition is an asynchronous method. The line marked as 2 will run before the callback function gets a chance to execute, so positionObject will still be undefined.

You need to move all code that depends on positionObject inside the callback to getCurrentPosition.