JavaScript navigator.userAgent obtains browser information case explanation

// All major browsers function getBrowser() {
    var u = navigator.userAgent;
 
    var bws = [{
        name: 'sgssapp',
        it: /sogousearch/i.test(u)
    }, {
        name: 'wechat',
        it: /MicroMessenger/i.test(u)
    }, {
        name: 'weibo',
        it: !!u.match(/Weibo/i)
    }, {
        name: 'uc',
        it: !!u.match(/UCBrowser/i) || u.indexOf(' UBrowser') > -1
    }, {
        name: 'sogou',
        it: u.indexOf('MetaSr') > -1 || u.indexOf('Sogou') > -1
    }, {
        name: 'xiaomi',
        it: u.indexOf('MiuiBrowser') > -1
    }, {
        name: 'baidu',
        it: u.indexOf('Baidu') > -1 || u.indexOf('BIDUBrowser') > -1
    }, {
        name: '360',
        it: u.indexOf('360EE') > -1 || u.indexOf('360SE') > -1
    }, {
        name: '2345',
        it: u.indexOf('2345Explorer') > -1
    }, {
        name: 'edge',
        it: u.indexOf('Edge') > -1
    }, {
        name: 'ie11',
        it: u.indexOf('Trident') > -1 && u.indexOf('rv:11.0') > -1
    }, {
        name: 'ie',
        it: u.indexOf('compatible') > -1 && u.indexOf('MSIE') > -1
    }, {
        name: 'firefox',
        it: u.indexOf('Firefox') > -1
    }, {
        name: 'safari',
        it: u.indexOf('Safari') > -1 && u.indexOf('Chrome') === -1
    }, {
        name: 'qqbrowser',
        it: u.indexOf('MQQBrowser') > -1 && u.indexOf(' QQ') === -1
    }, {
        name: 'qq',
        it: u.indexOf('QQ') > -1
    }, {
        name: 'chrome',
        it: u.indexOf('Chrome') > -1 || u.indexOf('CriOS') > -1
    }, {
        name: 'opera',
        it: u.indexOf('Opera') > -1 || u.indexOf('OPR') > -1
    }];
 
    for (var i = 0; i < bws.length; i++) {
        if (bws[i].it) {
            return bws[i].name;
        }
    }
 
    return 'other';
}
 
// System differentiation function getOS() {
    var u = navigator.userAgent;
    if (!!u.match(/compatible/i) || u.match(/Windows/i)) {
        return 'windows';
    } else if (!!u.match(/Macintosh/i) || u.match(/MacIntel/i)) {
        return 'macOS';
    } else if (!!u.match(/iphone/i) || u.match(/Ipad/i)) {
        return 'ios';
    } else if (!!u.match(/android/i)) {
        return 'android';
    } else {
        return 'other';
    }
}