## 题目 ### 模拟实现一个 Promise.finally ~~~js Promise.prototype.finally = function (callback) { let P = this.constructor; return this.then( value => P.resolve(callback()).then(() => value), reason => P.resolve(callback()).then(() => { throw reason }) ); }; ~~~ ## 摘自 [ 第 64 题：模拟实现一个 Promise.finally](https://www.muyiy.cn/question/async/64.html)