ウェブサイトの訪問者のデバイスとブラウザを検出する方法

console.log(window.navigator.userAgent);
// >> Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/120.0.0.0 Safari/537.36

let userAgentString = 'Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/120.0.0.0 Safari/537.36';
	
function deviceDetection(userAgentString) {
	let device = 'デスクトップ';

	if (
		/(android|bbd+|meego).+mobile|avantgo|bada/|blackberry|blazer|compal|elaine|fennec|hiptop|iemobile|ip(hone|od)|iris|kindle|lge |maemo|midp|mmp|mobile.+firefox|netfront|opera m(ob|in)i|palm( os)?|phone|p(ixi|re)/|plucker|pocket|psp|series(4|6)0|symbian|treo|up.(browser|link)|vodafone|wap|windows ce|xda|xiino/i.test(
			userAgentString
		)
	) {
		device = 'モバイル';
	}

	return device;
}

console.log(browserDetection(userAgentString));
// >> デスクトップ

let userAgentString = 'Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/120.0.0.0 Safari/537.36';

function browserDetection(userAgentString) {
	let browser = 'unknown';

	if (/Firefox/.*/.test(userAgentString) && !/Seamonkey/.*/.test(userAgentString))
		browser = 'Firefox';
	else if (/Seamonkey/.*/.test(userAgentString)) browser = 'Seamonkey';
	else if (
		/Chrome/.*/.test(userAgentString) &&
		!/Chromium/.*/.test(userAgentString) &&
		!/Edg.*/.*/.test(userAgentString)
	)
		browser = 'Chrome';
	else if (/Chromium/.*/.test(userAgentString)) browser = 'Chromium';
	else if (
		/Safari/.*/.test(userAgentString) &&
		!/Chromium/.*/.test(userAgentString) &&
		!/Edg.*/.*/.test(userAgentString)
	)
		browser = 'Safari';
	else if (/OPR/.*/.test(userAgentString)) browser = 'Opera 15+ (Blink-based engine)';
	else if (/Opera/.*/.test(userAgentString)) browser = 'Opera 15+ (Presto-based engine)';

	return browser;
}

console.log(browserDetection(userAgentString));
// >> Chrome