[ 源代码： node-when ]
软件包：node-when（3.7.8+ds-4）
Async tools and when() implementation for Node.js
A lightweight Promises/A+ and when() implementation, plus other async tools.
A when() function is responsible of triggering actions depending on the result of executing asynchronous actions, with submethods to check for any or all results, and handling exceptions.
Promises/A+ is a programming interface for asynchronous operations.
Node.js is an event-based server-side JavaScript engine.