Polyfill.io Name resolution pseudocode

polyio-names.js

// Functional Helper: When lambda returns an array, compose concat and map to return a flattened result.
// See https://gist.github.com/samgiles/762ee337dff48623e729 for an example
Array.prototype.flatMap = function(lambda) {
	return Array.prototype.concat.apply([], this.map(lambda));
};

// Mock, imagine this is some function that maps a modernizr test name to the polyfill.io nomenclature, if it doesn't map, 
// it must return the name as is. Must always be an array.
function getListOfPolyFillsForModernizrTest(name) {
	var mock = {
		'es5array': [
			'Array.prototype.every',
			'Array.prototype.filter',
			'Array.prototype.forEach',
			'Array.prototype.indexOf',
			'Array.prototype.lastIndexOf',
			'Array.prototype.map',
			'Array.prototype.some',
			'Array.prototype.reduce',
			'Array.prototype.reduceRight',
			'Array.isArray'
		],
		'requestanimationframe': [
			'Window.requestAnimationFrame'
		],
		'queryselector': [
			'Document.prototype.querySelector',
			'Document.prototype.querySelectorAll'
		]
	};

	return mock[name] || [name];
}

// Mock, imagine this is some function that maps Origami module names to Modernizr test names
// If it does not map, then return the name. (Must always be an array)
function getOrigamiModernizrNames(name) {
	var mock = {
		'o-gallery': [ 'queryselector', 'es5array' ],
		'o-ft-buttons': [ 'requestanimationframe', 'es5array' ]
	};

	return mock[name] || [name];
}

// An ordered list of name resolution functions. The first is called which transforms any origami module names
// then the second which transforms any modernizr names into polyfill.io names.
var polyfillLookUpServices = [
	function origami(name) {
		return getOrigamiModernizrNames(name);
	},
	function modernizr(name) {
		return getListOfPolyFillsForModernizrTest(name);
	}
];

// Apply the service to each polyfill name returning the transformed names.
function processListOfRequestedPolyfills(polyfills, service) {
	// Map each name using the service, and flatten into a single array of names.
	return polyfills.flatMap(function(polyfillName) {
		// Gets an array of polyfills that match the name
		return service(polyfillName);
	}).filter(function(polyfill, position, self) {
		// Filter out any duplicate polyfills
		return self.indexOf(polyfill) == position;
	});
}

function getPolyfills(polyfills) {
	// Keep track of the currently transformed polyfills.
	var transformedPolyfills = polyfills;
	
	// Apply each service to the current list of transformed polyfill names.
	polyfillLookUpServices.forEach(function(service) {
		transformedPolyfills = processListOfRequestedPolyfills(transformedPolyfills, service);
	});

	// return the final list of transformed polyfill names
	return transformedPolyfills;
}

getPolyfills(['es5array', 'requestanimationframe', 'o-gallery']);

// ["Array.prototype.every", "Array.prototype.filter", "Array.prototype.forEach", "Array.prototype.indexOf", "Array.prototype.lastIndexOf", "Array.prototype.map", "Array.prototype.some", "Array.prototype.reduce", "Array.prototype.reduceRight", "Array.isArray", "Window.requestAnimationFrame", "Document.prototype.querySelector", "Document.prototype.querySelectorAll"]

This seems to avoid the need to hard code an alias list into the config json for a polyfill

I think this is a big benefit, partly because the aliasing is a property of e.g. Modernizr, Origami, not an intrinsic property of the polyfill. Also it makes it clearer what the relationships when it's not a one-to-one correspondence between a polyfill and an alias.