Return a list (`[]`) of all unsupported browsers (`"${browser} ${version}"`) by a caniuse id (`"${id}"`)

getUnsupportedBrowsersByCaniuseId.js

const caniuse = require('caniuse-lite');

// return a list of all unsupported browsers by a caniuse id
function getUnsupportedBrowsersByCaniuseId (caniuseId) {
	// get compressed feature details from caniuse-lite by a caniuse id
	const featureDetails = caniuse.features[caniuseId];

	// if the feature exists
	if (featureDetails) {
		// get browsers stats for the feature
		const { stats: statsByBrowser } = caniuse.feature(featureDetails);

		// get a list of all unsupported browsers from the browsers stats
		const unsupportedBrowsers = Object.keys(statsByBrowser).reduce(
			(unsupportedBrowsers, browser) => {
				// get the browser stats organized by version
				const statsByBrowserVersion = statsByBrowser[browser];

				// get a list of all unsupported browser versions
				const unsupportedBrowserVersions = Object.keys(statsByBrowserVersion).reduce(
					(unsupportedBrowserVersions, version) => {
						// get the statistic for the specific browser version
						const statForBrowserVersion = statsByBrowserVersion[version];

						// if the feature is not fully supported by the specific browser version
						if (statForBrowserVersion[0] !== 'y') {
							// if the version is "all"
							if (version === 'all') {
								// if the agent has known versions then push every browser version query
								if ('versions' in Object(caniuse.agents[browser])) {
									caniuse.agents[browser].versions.filter(version => version !== null).forEach(version => {
										unsupportedBrowserVersions.push(`${browser} ${version}`);
									});
								}
								// otherwise, if the agent has no known versiosn, push a generic query
								else {
									unsupportedBrowserVersions.push(`${browser} > 0`);
								}
							}
							// otherwise, if the version is not "all", push the specific browser version query
							else {
								unsupportedBrowserVersions.push(`${browser} ${version}`);
							}
						}

						// return the list of all unsupported browser versions
						return unsupportedBrowserVersions;
					},
					[]
				);

				// push the unsupported browser versions to the list of all unsupported browsers
				unsupportedBrowsers.push(...unsupportedBrowserVersions);

				// return the list of all unsupported browsers
				return unsupportedBrowsers;
			},
			[]
		);

		// return the list of all unsupported browsers
		return unsupportedBrowsers;
	}

	// otherwise, return a generic query for all browsers
	return [ '> 0%' ];
}