Merge pull request #4108 from shaedrich/promise

Add topic "Promise"

topics/promise/index.md

@@ -0,0 +1,10 @@
+---
+topic: promise
+display_name: Promise
+short_description: A promise is an object returned by an asynchronous function, which represents the current state of the operation.
+related: future, async-await, callback, deferred, coroutines, fiber, concurrency
+wikipedia_url: https://en.wikipedia.org/wiki/Futures_and_promises
+created_by: Barbara Liskov, Liuba Shrira, Mark S. Miller, Dean Tribble, Rob Jellinghaus, Daniel P. Friedman
+released: 1988
+---
+A **promise** is an object returned by an asynchronous function, which represents the current state of the operation. At the time the promise is returned to the caller, the operation often isn't finished, but the promise object provides methods to handle the eventual success or failure of the operation.