<button style="font-size:40px" onclick="startGeo()">start geo!</button>

var storedLocation = null;

function startGeo() {
  alert( storedLocation );

  navigator.geolocation.getCurrentPosition(
    function( geo ){
      storedLocation =  geo.coords.latitude + ' / ' + geo.coords.longitude ;
      alert( storedLocation );
    },
    function( err ){
      alert( err.message );
    },
    {
      enableHighAccuracy : true,
      maximumAge : 30000,
      timeout : 20000
    }
  );
}

startGeo();