Simple ES6+ Polyfill test. Transpile using babel.

polyfill-test.js

window.POLYFILL_ALL_THE_THINGS = {
	reduce: ['foo', 'bar', 'baz'].reduce( ( acc, v ) => {
		return { ...acc, [`${v}_key`]: `${v}_value` };
	}, [] ),
	reduceRight: ['foo', 'bar', 'baz'].reduceRight( ( acc, v ) => {
		return { ...acc, [`${v}_key`]: `${v}_value` };
	}, {} ),
	map: ['foo', 'bar', 'baz'].map( str => {
		return str += ' 1';
	} ),
	filter: ['foo', 'bar', 'baz'].filter( str => {
		return str.includes( 'ba' );
	} ),
	promise: new Promise( ( resolve ) => {
		setTimeout( () =>  {
			resolve( 'foo' );
		}, 300 );
	} ),
};

const {
	reduce,
	reduceRight,
	filter,
	map,
	promise,
} = window.POLYFILL_ALL_THE_THINGS;

const consoleStyle = 'background:#ffcc3d;color:#ffffff;font-size:16px';

console.log( '%cnew Promise():', consoleStyle );
promise.then( r => {
	console.log( `Promise resolved: ${r}` );
} );

console.log( '%carray.reduce():', consoleStyle );
console.log( reduce );
console.log( '%carray.reduceRight():', consoleStyle );
console.log( reduceRight );
console.log( '%carray.filter():', consoleStyle );
console.log( filter );
console.log( '%carray.map():', consoleStyle );
console.log( map );

/* 
 * Expected output - https://tinyurl.com/y5dtn8u9
 * > 1%
 * last 2 versions
 * Firefox ESR
 * IE 11
 */