How to create a timer that starts at 10 and goes to 1 in 3 seconds?

Question

I am a web designer, and I am not much of a developer. I need to create a timer that counts down quickly from 10 to 1 when a user scrolls to the part of the page where that div appears. I'm planning on using a large bold font with nothing but "10" in it, that scrolls through the numbers 9-2 and then stops at 1. (ie, I don't need a timer that also has hours, colons, or minutes.

Anyone have any ideas? Thank you ahead of time!!!!

Answer 1

This is done with simple javascript and one span element.

var number = 10;
var counter = document.getElementById('counter');
function countDown() {
   counter.innerHTML = '' + number;
   number--;
   if(number > 0) {
      setTimeout(function() { countDown(); }, 1000.0/3);
   }
}
countDown();

<span id="counter"></span>

That will trigger counter after it pops into visible part of the screen on scroll. Note that I've added two items, just for testing purpose.

var elements = {
    counterA: {
            from: 10,
            to: 0,
            counterStarted: false,
            dom: document.getElementById('counterA'),
            speed: 1000.0/3
    },
    counterB: {
            from: 400,
            to: 49,
            counterStarted: false,
            dom: document.getElementById('counterB'),
            speed: 1000.0/40
    }
};

function countDown(el) {
    el.dom.innerHTML = '' + el.from;
    el.from--;
    if(el.from > el.to) {
            setTimeout(function() { countDown(el); }, el.speed);
    }
}

function triggerCounterIfVisible(el) {
    if(el.counterStarted) return;

    var elemTop = el.dom.getBoundingClientRect().top;
    var elemBottom = el.dom.getBoundingClientRect().bottom;

    var isVisible = (elemTop >= 0) && (elemBottom <= window.innerHeight);
    if (isVisible) {
            el.counterStarted = true;
            countDown(el);
    }
}

window.onscroll = function() {
    for(var el in elements) {
            triggerCounterIfVisible(elements[el]);
    }
};

<div style="height: 3000px"></div>
<hr />
<p>Counter: <span id="counterA"></span></p>

<div style="height: 3000px"></div>
<hr />
<p>Counter: <span id="counterB"></span></p>

<div style="height: 3000px"></div>