The Promises/A+ specification is one of the smallest specifications. Hence, implementing it is the best way to understand it. The following answer by Forbes Lindesay walks us through the process of implementing the Promises/A+ specification, Basic Javascript promise implementation attempt. However, when I tested it the results were not satisfactory:
ā 109 tests passed
ā 769 tests failed
Clearly, the Promises/A+ specification is not as easy to implement as it seems. How would you implement the specification and explain your code to a novice? Forbes Lindesay does an excellent job explaining his code but unfortunately his implementation is incorrect.