實做一個 promise finally

javascript-promise-finally.js

// http://bluebirdjs.com/docs/api/finally.html

Promise.prototype.end = function(fn) {
  return new Promise((resolve, reject)=>{
    this.then((res)=>{
        fn(false, res)
        resolve()
    })
    .catch((er)=>{
        fn(true, er)
        reject()
    })
  })
}


promise.end((err, res)=>{
    if (err) {
        // equal .catch
    }
})