KeyMemberQ

KeyMemberQ[assoc, form] yields True if a key in the association assoc matches form, and False otherwise.

KeyMemberQ[form] represents an operator form of KeyMemberQ that can be applied to an expression.

Examples

KeyMemberQ[<|"a" -> 1, "b" -> 2|>, "a"]
(* True *)

Please visit the official Wolfram Language Reference for more details.