rickroll-once.js

const RICKROLL = "https://www.youtube.com/watch?v=oHg5SJYRHA0";
const RICKROLL_DAY = 1;
const RICKROLL_MONTH = 4;
if(Storage && window.localStorage && window.localStorage instanceof Storage) {
    // Check if it's 1st of April
    var date = new Date();
    // Note that months are zero indexed
    if(date.getDate() == RICKROLL_DAY && date.getMonth() == RICKROLL_MONTH-1) {
        // If local storage does not work, rickroll will simply never occur
        // this is a safety measure to prevent people being rickrolled forever
        localStorage.LOCAL_STORAGE_WORKS = true;
        // This will be called as an on click handler for anchor elements
        function rickroller(event) {
            console.info("Rickrolling!");
            if(localStorage.RICKROLLED_AT) {
                console.warn("Rickrolling canceled!");
                return true;
            }
            // Remember that user was rickrolled
            localStorage.RICKROLLED_AT = new Date().getTime();
            event.preventDefault();
            // New tab links go to a new tab
            if(this.target=="_blank") {
                window.open(RICKROLL);
            }
            else
                window.location.href = RICKROLL;
            return false;   
        }
        
        if(localStorage.LOCAL_STORAGE_WORKS && !localStorage.RICKROLLED_AT) {
            var ar=[];
            console.info("Initiating rickroll!");
            // Get all links as an array
            ar.push.apply(ar, document.querySelectorAll("a"));

            ar.forEach((link)=>{
                // Skip links that do not lead outside
                if(link.href.indexOf("http")!=0&&link.href.indexOf("//")!=0)  {
                    console.log(link.href, link.href.indexOf("http"), link.href.indexOf("//"));
                    return;                
                }
                link.addEventListener("click", rickroller);   
                // This was used to test if this code is executing, do not uncoment
                //link.appendChild(new Text("VOLE"));       
            });
        }
        else {
            console.info("Already rickrolled!");
        }
    }
    else {
        console.info("Not a good day for rickrolling.", date.getDate(),date.getMonth());
    }
}
else {
    console.warn("Local storage not supported by the browser.");
}