Watches whether the url is healthy (200)

jonsnow.js

(() => {
    let endWatch = () => {};
    const log = (msg, color) => {
        console.log('%c Jon Snow %c  ' + msg, 'color: white;background: black;padding: 5px 2px;', 'color:' + color);
    };
    log('Hello there.', 'green');
    window.JONSNOW = {
        'watch': (url, interval) => {
            window['JONSNOW'] && window.JONSNOW.end();
            interval = interval || 60 * 1000;
            if (interval < 60 * 1000) {
                log('its too frequent. Such a short span of of life', 'orange');
            }
            const intervalId = setInterval(() => {
                var oReq = new XMLHttpRequest();
                oReq.addEventListener("load", () => {
                    if (oReq.status === 200) {
                        log('it is alive', 'orange')
                    } else {
                        log('it might be dead', 'red')
                    }
                });
                oReq.open("GET", url);
                oReq.send();
            }, interval);
            endWatch = () => {
                clearInterval(intervalId);
                log('My watch has ended.', 'red');
                window.removeEventListener('beforeunload', endWatch);
            };
            window.addEventListener('beforeunload', endWatch);
            log('My watch has started.', 'green');
            return endWatch;
        },
        'end': () => {
            endWatch()
        }
    };
    return window.JONSNOW;
})().watch('url_to_check', 2 * 60 * 1000);