"reason" is a value that indicates why a promise was rejected.Ī promise must be in one of three states: pending, fulfilled, or rejected."exception" is a value that is thrown using the throw statement."value" is any legal JavaScript value (including undefined, a thenable, or a promise)."thenable" is an object or function that defines a then method."promise" is an object or function with a then method whose behavior conforms to this specification.Future work in companion specifications may touch on these subjects.
Historically, Promises/A+ clarifies the behavioral clauses of the earlier Promises/A proposal, extending it to cover de facto behaviors and omitting parts that are underspecified or problematic.įinally, the core Promises/A+ specification does not deal with how to create, fulfill, or reject promises, choosing instead to focus on providing an interoperable then method. Although the Promises/A+ organization may occasionally revise this specification with minor backward-compatible changes to address newly-discovered corner cases, we will integrate large or backward-incompatible changes only after careful consideration, discussion, and testing.
As such, the specification should be considered very stable. This specification details the behavior of the then method, providing an interoperable base which all Promises/A+ conformant promise implementations can be depended on to provide. The primary way of interacting with a promise is through its then method, which registers callbacks to receive either a promise's eventual value or the reason why the promise cannot be fulfilled. An open standard for sound, interoperable JavaScript promises-by implementers, for implementers.Ī promise represents the eventual result of an asynchronous operation.
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