Defines an interface for something that might be an observer if a notify() is present
Add an item to an array list if it doesn't already exist. Returns true if added, false if not and already exists in the array.
See if an array contains something
Create a promise that resolves after a certain number of milliseconds
It is strongly recommended you pass the excalibur clock so delays are bound to the excalibur clock which would be unaffected by stop/pause.
Used for exhaustive checks at compile time
Find the screen position of an HTML element
Remove an item from an list