*finally-polyfill.md

finally-polyfill

A tiny 153-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

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=function(n){if("function"!=typeof n)return this.then(n,n);var t=this.constructor||Promise;return this.then(function(r){return t.resolve(n()).then(function(){return r})},function(r){return t.resolve(n()).then(function(){throw r})})};

package.json

{
  "version": "0.1.0",
  "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"
}