script loading

The maps APIs are loaded with a script.

The script defines a global variable/object, that is the map and all its functions (google.map or ol)

There are two ways to load a script, synchronously and asynchronously:

asynchronously means that your page will continue doing what a page has to do, while the script is being loaded

synchronously means that your page will stop everything and wait for the script to be loaded in order to continue