Why doesn't Google maps load right away?

Question

JavaScript

The situation is this, in general, there are tabs, in one of the tabs Google maps are loaded, but! For some reason they look like this.

If you open the firebug, the map starts to appear, what kind of nonsense?
The map is connected via the API, that is, at the end of the body

<script src="https://maps.googleapis.com/maps/api/js?key=мой-ключ-от-апи&libraries=places"></script>

and in the place where the map is initialized

<script>
window.onload = function(){
  initMap();
}
</script>

But it is not at all clear why this is happening? Nothing in the Javascript console, empty!

Answer 1

and if so?

document.observe
(
  "dom:loaded", 
  function()
  {
    // put your code here
  } 
);