This variable is global in scope and is used to hold a DS map when used in the Asynchronous Events, and -1 at all other times. The actual contents of the DS map will depend on the type of asynchronous event callback, as well as the function that was used to trigger the event, so refer to the individual pages for those events for full details of all the possible DS map contents.
async_load;
sprite = sprite_add("site.com/path/image.png", 16, true, true, 0, 0);
The above code would be called in an event to load a sprite from an external URL. This would then trigger the Image Loaded Asynchronous Event, where you would parse the async_load map:
if ds_map_find_value(async_load, "id") == sprite
{
if (ds_map_find_value(async_load, "status") >= 0)
{
sprite_index = sprite;
}
}
The above code will first check the ID of the async_load map, then check the status of the callback. If the value is greater than or equal to 0 (signalling success) the result from the callback will then be used to set the sprite index of the instance to the newly loaded image.