从回调中获取值 function

Question

I'm trying to return a value from a callback function and assign it to a variable, though am struggling to work it out - any help would be really appreciated....

var latlng1;

function getLocation(){
  navigator.geolocation.getCurrentPosition (function (position){
    coords = position.coords.latitude + "," + position.coords.longitude;
    callback();         
  })
}

//how can I assign the coords value from the callback to variable latlng1 with global scope?
getLocation (function(){
  //alert(coords);
  return coords;
})

// -----------
//I'm trying something like this....but no joy
latlng1 = getLocation (function(){
  return coords;
}

Answer 1

I'm confused as whether or not you want the callback to have access to the coords value or to simply return it from the getLocation function. If it's just to have coords available to the callback then pass it as a parameter.

function getLocation(callback) {
  navigator.geolocation.getCurrentPosition (function (position){
    var coords = position.coords.latitude + "," + position.coords.longitude;
    callback(coords);         
  })
}

getLocation (function(coords){
  alert(coords);
})

On the other hand if it's to have it assigned to the return of getLocation then that's not possible. The getCurrentPosition API is asynchronous and hence you can't synchronously return it from the getLocation method. Instead you need to pass the call back which wants to use coords .

EDIT

OP said they just want the coords value in latlng1 . Here is how you accomplish that

var latlng1;
function getLocation() {
  navigator.geolocation.getCurrentPosition (function (position){
    var coords = position.coords.latitude + "," + position.coords.longitude;
    latlng1 = coords; 
  })
}

Note though that this doesn't change the asynchronous nature of the API. The variable latlng1 won't have the coords value until the async call completes. Because this version doesn't use a callback you have no way of knowing when that completes (other than checking latlng1 for undefined

Answer 2

How about:

var latlng1;

function getLocation(){
  navigator.geolocation.getCurrentPosition (function (position){
    latlng1 = position.coords.latitude + "," + position.coords.longitude;
    callback();         
  })
}

getLocation (function(){
  alert(latlng1);
})

Answer 3

You can pass coords to the callback call, and define a parameter for it in the callback. It's easier to read than to try to explain:

var latlng1;

function getLocation(callback){
  navigator.geolocation.getCurrentPosition (function (position){
    coords = position.coords.latitude + "," + position.coords.longitude;
    callback(coords);         
  })
}

//how can I assign the coords value from the callback to variable latlng1 with global scope?
getLocation (function(coords){
  //alert(coords);
  return coords;
})