Assigns a unique ID for the specified reference type value, represented by an integer.
the non-null object, array, or non-shared symbol to assign the ID.
object
array
symbol
an immutable ID specific for this object. If the object has already been assigned an ID, this function will return the prior assigned ID.
obj is not an object or array, or obj is null or shared symbol.
obj
null
Assigns a unique ID for the specified reference type value, represented by an integer.