Test if we have an internet connection with JS

test-internet-connection.js

function testConnection() {
	var url = location.href.match(/^https?\:/i) ? '/' : 'https://google.com'
	var rand =  parseInt(Math.ceil(Math.random()*Math.pow(10, 14))).toString(16)
	var retry = ms => setTimeout(() => testConnection(), ms || 5000)
	var notify = msg => document.body.innerHTML = `<h1 style="font-size:300%;position:fixed;top:40%;width:100%;text-align:center;">${msg}</h1>`
	var handleResp = (err, msg) => {
		console.log(err, new Date, msg)
        notify(msg)
		retry()
    }

    fetch(url + '?' + rand, {mode: 'no-cors'} )
		.then( () => handleResp(null, 'Connected!') )
		.catch( e => handleResp(e, 'Disconnected! Retry...') )
}

testConnection()