*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"
}

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