Javascript function variable scope passthrough geolocation

Question

I'm just trying to get variables out of the geolocation.getCurrentPosition function from HTML5. However, I'm having a lot of difficulties getting my variables to be defined outside of the function.

The function works using the code below:

<script>
var latitude;
var longitude;
var accuracy;
var altitude;
var altitudeAccuracy;
var heading;
var speed;

if (navigator.geolocation){
  navigator.geolocation.getCurrentPosition(  
    function (position) {
      latitude = position.coords.latitude;
      longitude = position.coords.longitude;
      alert(longitude)
      accuracy = position.coords.accuracy;
      altitudeAccuracy = position.coords.altitudeAccuracy;
      heading = position.coords.heading;
      speed = position.coords.speed;
    }
  );
}

// alert(latitude);

Here I see the alert(longitude) return a numerical value. However when I comment that line out, and uncomment alert(latitude) -- I get an "undefined" alert.

Any help would be greatly appreciated! Thanks.

epascarello · Accepted Answer · 2013-01-07 16:17:31Z

4

Because getCurrentPosition is an asynchronous call.

You need to wait for the callback to fire before you can access the values it retrieves.

function nextStep(){
    alert(latitude);
}

navigator.geolocation.getCurrentPosition(  
    function (position) {
      latitude = position.coords.latitude;
      longitude = position.coords.longitude;
      alert(longitude)
      accuracy = position.coords.accuracy;
      altitudeAccuracy = position.coords.altitudeAccuracy;
      heading = position.coords.heading;
      speed = position.coords.speed;
      nextStep();
    }
);

answered Jan 7, 2013 at 16:17

epascarello

208k20 gold badges206 silver badges246 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Ben McCormick · Accepted Answer · 2013-01-07 16:25:54Z

1

getCurrentPosition is an asynchronous call

In javascript concurrency works with a "run to completion" model. That means that all code in the current function will complete before it moves on to the next execution context. In your original code, the code will execute in this order:

variable definitions
getCurrentPosition initialized
alert(latitude)
script completes

and then it will move on to the next execution context and run your callback function, at which time the variables will be set and the other alert will be run. You'll need to run your alert in the callback if you want to ensure that the variables have been set first

answered Jan 7, 2013 at 16:25

Ben McCormick

25.8k12 gold badges56 silver badges71 bronze badges

Collectives™ on Stack Overflow

Javascript function variable scope passthrough geolocation

2 Answers 2

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related