Drop in logging solution for debugging where DevTools isn't available.

exlog.js

var lastMsg
function exlog (text) {
    var popup = document.getElementById('xlog-popup')
    if (!popup) {
        popup = document.createElement('div')
        Object.assign(popup.style, {
            width: '100%',
            height: '100%',
            top: 0,
            left: 0,
            position: 'absolute',
            zIndex: 1000000,
            padding: '20px',
            pointerEvents: 'none',
            background: 'rgba(255, 255, 255, 0.5)'
        })
        popup.setAttribute('id', 'xlog-popup')
        document.body.appendChild(popup)
    }

    if (lastMsg === text) {
        var msg = document.getElementById('xlog-popup').querySelector('p:last-child')
        var counter = msg.querySelector('span')

        if (!counter) {
            counter = document.createElement('span')
            counter.style.paddingLeft = '10px'
            msg.appendChild(counter)
        }

        counter.innerText = (parseInt(counter.innerText) || 0) + 1
    } else {
        var msg = document.createElement('p')
        Object.assign(msg.style, {
            color: '#c00',
            fontSize: '20px'
        })
        msg.innerText = text
        lastMsg = text

        popup.appendChild(msg)
    }
}

window.onerror = function errorExlog (err, source, lineno, colno, error) {
    exlog('Error: ' + err + ' source: ' + source + ' line#' + lineno + ':' + colno + ' : ' + error)
}