Create a simple 10 second countdown

参考：https://stackoverflow.com/questions/55224963/adding-a-button-to-a-javascript-countdown

// Set the date we're counting down to
var countDownDate = new Date(Date.now() + 20000).getTime();
// Update the count down every 1 second
var x = setInterval(function() {
// Get todays date and time
var now = new Date().getTime();
// Find the distance between now and the count down date
var distance = countDownDate - now;
// Time calculations for days, hours, minutes and seconds
var days = Math.floor(distance / (1000 * 60 * 60 * 24));
var hours = Math.floor((distance % (1000 * 60 * 60 * 24)) / (1000 * 60 * 60));
var minutes = Math.floor((distance % (1000 * 60 * 60)) / (1000 * 60));
var seconds = Math.floor((distance % (1000 * 60)) / 1000);
// Output the result in an element with id="demo"
document.getElementById("demo").innerHTML = days + " days, " + hours + " hours, " +
minutes + " minutes, & " + seconds + " seconds";
// If the count down is over, write some text 
if (distance < 0) {
clearInterval(x);
document.getElementById("demo").innerHTML = '<a href="https://facebook.com">We\'re Live on Facebook!</a>';
}
}, 1000);
视图页面的
<p id="demo" class="countdown-live" style="text-align:center;"></p>

点击链接（按钮），进行倒数，倒数结束进行按钮的显示。