*finally-polyfill.md

finally-polyfill

A tiny ~150-byte polyfill for Promise.prototype.finally.

Useful for browsers that support Promise but not the .finally() method.

Usage

npm install finally-polyfill

It's a polyfill, so you can import, require() or drop it in a script tag - all the same.

import 'finally-polyfill';
Promise.reject('oops').finally(() => { /* ... */ })

<script src="/path/to/finally-polyfill.min.js"></script>

License

MIT

finally-polyfill.js

if (!Promise.prototype.finally) {
  Promise.prototype.finally = function(callback) {
    if (typeof callback !== 'function') {
      return this.then(callback, callback);
    }
    const P = this.constructor || Promise;
    return this.then(
      value => P.resolve(callback()).then(() => value),
      err => P.resolve(callback()).then(() => { throw err; })
    );
  };
}

finally-polyfill.min.js

Promise.prototype.finally||(Promise.prototype.finally=function(t){if("function"!=typeof t)return this.then(t,t);const e=this.constructor||Promise;return this.then(o=>e.resolve(t()).then(()=>o),o=>e.resolve(t()).then(()=>{throw o}))})

package.json

{
  "version": "0.2.0",
  "name": "finally-polyfill",
  "main": "finally-polyfill.min.js",
  "author": "Jason Miller <jason@developit.ca>",
  "repo": "gist:d970bac1843",
  "homepage": "https://gist.github.com/developit/d970bac18430943e4b3392b029a2a96c",
  "scripts": { "prepack": "mv *finally-polyfill.md README.md", "postpack": "mv README.md *finally-polyfill.md" },
  "license": "MIT"
}

For developers who still need to support IE11 and Chrome 49, this is what you need!

For developers who still need to support IE11 and Chrome 49, this is what you need!

I had to replace arrow functions to get it to work in IE11.

If you use create-react-app or similar tool (with browserlists config ie: 11), babel will do this transform for you