When.js 3.4.0 发布了，改进内容包括：
New when.filter for filtering arrays of promises. when.map and when.filter now provide the array index as the second param to their mapping and filtering functions.
when/keys.map now provides the associated key to its mapping function.
Smaller ES6 shim.
When.js 是 cujojs 的轻量级的 Promises/A 和 when() 实现，从 wire.js 的异步核心和 cujojs 的 IOC 容器派生而来。包含很多其他有用的 Promiss 相关概念，例如联合多个 promiss、mapping 和减少 promises 集合以及 timed promises 等。 | 
