返回值回调函数？

Question

I'm having some trouble with function callbacks, specifically with the HTML5 geolocation API. I'm a little new to Js as well. The function:

function getInfo()
{
    navigator.geolocation.getCurrentPosition(getPos);
}

takes a callback parameter of a function that gets the position passed into it.

function getPos(position)
{
PositionObj.lat = position.coords.latitude;
PositionObj.lon = position.coords.longitude;
}

I created a "location" object to store the coordinates, and I'm having trouble returning them.

var PositionObj = 
{
lat:null,
lon:null,
returnLat: function()
             {
             return this.lat;
             },
returnLon: function()
             {
             return this.lon;
             }
};


function printStuff()
{
getInfo();
console.log(PositionObj.returnLat());
}

EDIT: Syntax mistakes fixed. When I call printStuff(), I still get "null."

Answer 1

• To pass the callback, use just getPos instead of calling the function right away.
• Use proper syntax to declare properties in PositionObj .

PositionObj = {
    lat: null,
    lon: null,
}

Answer 2

Your PositionObj literal is incorrect. the initial properties should be set with colons:

{ lat: '', lon: '' }

Answer 3

The callback should tell you that the request to get position information is asynchronous. This means that getInfo() does NOT set the values instantly, and therefore the following line cannot access the "new" values.

Anything that relies on the result of an asynchronous function MUST be within the callback itself.