NodeJS module to create polyfill bundles tailored to individual user-agents

npm install polyfill-library --save

const polyfillLibrary = require('polyfill-library');

const polyfillBundle = polyfillLibrary.getPolyfillString({
	uaString: 'Mozilla/5.0 (Windows; U; MSIE 7.0; Windows NT 6.0; en-US)',
	minify: true,
	features: {
		'es6': { flags: ['gated'] }
	}
}).then(function(bundleString) {
	console.log(bundleString);
});

Get a list of all the polyfills which exist within the collection of polyfill sources.

Returns a Promise which resolves with an array of all the polyfills within the collection.

Get the metadata for a specific polyfill within the collection of polyfill sources.

• @param {String} featureName - The name of a polyfill whose metadata should be returned.

Returns a Promise which resolves with the metadata or with undefined if no metadata exists for the polyfill.

Create an options object for use with getPolyfills or getPolyfillString.

• @param {object} opts - Valid keys are uaString, minify, unknown, excludes, rum and features.
• @param {Boolean} [opts.minify=true] - Whether to return the minified or raw implementation of the polyfills.
• @param {'ignore'|'polyfill'} [opts.unknown='polyfill'] - Whether to return all polyfills or no polyfills if the user-agent is unknown or unsupported.
• @param {Object} [opts.features={}] - Which features should be returned if the user-agent does not support them natively.
• @param {Array<String>} [opts.excludes=[]] - Which features should be excluded from the returned object.
• @param {String} [opts.uaString=''] - The user-agent string to check each feature against.
• @param {Boolean} [opts.rum=false] - Whether to include a script that reports anonymous usage data in the polyfill bundle.

Returns an object which has merged opts with the defaults option values.

Given a set of features that should be polyfilled in 'opts.features' (with flags i.e. {<featurename>: {flags:Set[<flaglist>]}, ...}), determine which have a configuration valid for the given opts.uaString, and return a promise of set of canonical (unaliased) features (with flags) and polyfills.

• @param {object} opts - Valid keys are uaString, minify, unknown, excludes, rum and features.
• @param {Boolean} [opts.minify=true] - Whether to return the minified or raw implementation of the polyfills.
• @param {'ignore'|'polyfill'} [opts.unknown='polyfill'] - Whether to return all polyfills or no polyfills if the user-agent is unknown or unsupported.
• @param {Object} [opts.features={}] - Which features should be returned if the user-agent does not support them natively.
• @param {Array<String>} [opts.excludes=[]] - Which features should be excluded from the returned object.
• @param {String} [opts.uaString=''] - The user-agent string to check each feature against.
• @param {Boolean} [opts.rum=false] - Whether to include a script that reports anonymous usage data in the polyfill bundle.

Returns a Promise which resolves to an Object which contains the canonicalised feature definitions filtered for UA.

Create a polyfill bundle.

• @param {object} opts - Valid keys are uaString, minify, unknown, excludes, rum and features.
• @param {Boolean} [opts.minify=true] - Whether to return the minified or raw implementation of the polyfills.
• @param {'ignore'|'polyfill'} [opts.unknown='polyfill'] - Whether to return all polyfills or no polyfills if the user-agent is unknown or unsupported.
• @param {Object} [opts.features={}] - Which features should be returned if the user-agent does not support them natively.
• @param {Array<String>} [opts.excludes=[]] - Which features should be excluded from the returned object.
• @param {String} [opts.uaString=''] - The user-agent string to check each feature against.
• @param {Boolean} [opts.rum=false] - Whether to include a script that reports anonymous usage data in the polyfill bundle.
• @param {Boolean} [opts.stream=false] - Whether to return a stream or a string of the polyfill bundle.

Returns a polyfill bundle as either a utf-8 ReadStream or as a Promise of a utf-8 String.

To use this package in an AWS Lambda function, you need to include the distribution Polyfills located in ./node_modules/polyfill-library/polyfills/__dist in the root directory of your Lambda. In AWS, Lambdas are executed in the /var/task/... directory. Therefore, during execution, the directory where the polyfills will be located will be /var/task/polyfill-library/__dist.

The following snippet will allow us to copy the polyfills to our already compiled Lambda. To do this, we will first install the necessary dependencies.

yarn add -D make-dir fs-extra

Once the dependencies are installed, we will create the file with the script at /scripts/polyfills-serverless.mjs and replace YOUR_BUNDELED_LAMBDA_DIRECTORY with the directory that contains our packaged Lambda.

In the example, we will use the directory ./.serverless_nextjs/api-lambda, which is the one used when using Serverless Next.js.

import { copySync } from 'fs-extra/esm';
import makeDir from 'make-dir';

const DIR_POLYFILLS = './node_modules/polyfill-library/polyfills/__dist';
// const DIR_SERVERLESS = 'YOUR_BUNDELED_LAMBDA_DIRECTORY/polyfills/__dist';
const DIR_SERVERLESS = './.serverless_nextjs/api-lambda/polyfills/__dist';

const paths = await makeDir(DIR_SERVERLESS);
console.log(`The directory ${paths} is created successfully.`);

try {
  console.log('Copying polyfills to serverless directory...');
  copySync(DIR_POLYFILLS, DIR_SERVERLESS, { overwrite: false });
  console.log('Polyfills copied successfully!');
} catch (err) {
  console.error(err);
}

To execute the script, you will need to run the following command:

node ./scripts/polyfills-serverless.mjs

Development of polyfill-library happens on GitHub. Read below to learn how you can take part in contributing to Polyfill.io.

Read our contributing guide to learn about our development process, how to propose bugfixes and improvements, and how to build and test your changes.

# To test on BrowserStack you will need to have a BrowserStack account
# We test pull-requests using BrowserStack
npm run test-all-polyfills # Run the tests for all polyfills using BrowserStack
npm run test-polyfills -- --features=Array.from # Run the tests for Array.from
npm run test-polyfills -- --features=Array.from --browserstack # Run the tests for Array.from using BrowserStack

Polyfill-library is MIT licensed.