if (document.referrer === 'https://news.ycombinator.com/') window.location = 'https://cdn.jwz.org/images/2016/hn.png' Or something along those lines should

if (document.referrer === 'https://news.ycombinator.com/') window.location = 'https://cdn.jwz.org/images/2016/hn.png' Or something along those lines should work.