Constant SYSTEM_OF_JS 

pub const SYSTEM_OF_JS: &str = "function systemOf(ua, platform, uaPlatform, touch) { \
var says = function (w) { return ua.indexOf(w) !== -1; }; \
var starts = function (p) { return platform.indexOf(p) === 0; }; \
if (says('iPhone') || says('iPad') || says('iPod') || says('Android') || uaPlatform === 'Android' || uaPlatform === 'iOS' || starts('iPhone') || starts('iPad') || starts('iPod') || (platform === 'MacIntel' && touch > 1)) return 'phone'; \
if (says('CrOS') || uaPlatform === 'Chrome OS' || uaPlatform === 'ChromeOS') return 'chromeos'; \
if (uaPlatform === 'Windows' || starts('Win') || says('Windows')) return 'windows'; \
if (uaPlatform === 'macOS' || starts('Mac') || says('Macintosh')) return 'macos'; \
if (uaPlatform === 'Linux' || starts('Linux') || says('X11') || says('Linux')) return 'linux'; \
return 'unknown'; }";

system_of in JavaScript: systemOf(userAgent, platform, uaPlatform, maxTouchPoints) returns System::name. landing_page::the_os_script_reads_the_system_as_the_app_does holds the two to the same answers for every visitor of the fixture.