xkcd permalink bookmarklet (navigates to permalink URL)

xkcd-permalink.js

BOOKMARKLET_NAME = 'xkcd-permalink.js';

function main() {
    var prev = $('a[rel="prev"]')[0].href;
    var parts = prev.split('/');
    if (parts.length !== 5) {
        fail('Expected exactly 4 slashes in "prev" link URL, e.g. https://www.xkcd.com/1000/. Actual URL: ' + prev);
    }
    if (!Number.isInteger(+parts[3])) {
        fail('URL segment before last slash must be an integer. Actual: ' + parts[3]);
    }
    parts[3] = (+parts[3] + 1) + '';
    location.href = parts.join('/');
}

function fail(reason) {
    alert('Bookmarklet "' + BOOKMARKLET_NAME + '" failed: ' + reason);
    throw reason;
}

main();