Null Coalescing Operator

The ?? operator returns its left operand if it is not null, otherwise it returns its right operand. It is right-associative.

var name = Data.user.name ?? "Unknown"    # "Unknown" if name is null

Chaining

Multiple ?? operators can be chained. Evaluation proceeds left to right, returning the first non-null value:

var first = null ?? null ?? "found"       # "found"
var value = Data.primary ?? Data.fallback ?? "default"

Comparison with or

?? checks strictly for null, while or checks for any falsy value. Use ?? when you want to preserve legitimate falsy values like 0, "", or false:

var x = 0 ?? "default"     # 0 (not null, so 0 is kept)
var y = 0 or "default"     # "default" (0 is falsy)