学习链接

网道教程：Promise

Promise.prototype.finally

promise
.finally(() => {
    // 语句
});
// 等同于
promise
.then(
    result => {
        // 语句
        return result;
    },
    error => {
        // 语句
        throw error;
    }
);

实现

Promise.prototype.myFinally = (callback) => {
    return this.then(
        value => Promise.resolve(callback()).then(() => value),
        reason => Promise.resolve(callback()).then(() => { throw reason; })
    )
};