MediaWiki:Common.js

// Any JavaScript here will be loaded for all users on every page load.

var today = new Date();
var month = today.getMonth() + 1; // 1–12
var day = today.getDate();

var prankMonth = 10;  // October
var prankDay = 12;    // test day

var pageName = mw.config.get('wgPageName');
var namespace = mw.config.get('wgNamespaceNumber'); // MediaWiki namespace = -8

if (month === prankMonth && day === prankDay) {
    // Skip AF pages & MediaWiki namespace (like Common.js)
    if (!pageName.startsWith('AF:')) {

        // Explicitly handle Main_Page
        if (pageName === 'Main_Page') {
            window.location.href = '/wiki/AF:Main_Page';
        } else {
            window.location.href = '/wiki/AF:' + pageName;
        }

    }
}