How to create javascript countdown?

I want to create a javascript live countdown. Almost like statistics site has. enter image description here

I have created the html file but I am not good at javascript so I need your help.

<table>
            <tbody><tr><td class="counter"><div id="cp1">7,795,022,199</div></td>
                <td class="data_name"><b>Current population</b></td></tr>
            <tr><td class="counter"><div id="cp2">3,931,870,264</div></td>
                <td class="data_name">Current male population <span id="cp4">(50.4%)</span></td></tr>
            <tr><td class="counter"><div id="cp3">3,863,151,936</div></td>
                <td class="data_name">Current female population <span id="cp5">(49.6%)</span></td></tr>
            <tr><td class="counter"><div id="cp6">52,128,438</div></td>
                <td class="data_name">Births year to date</td></tr>
            <tr><td class="counter"><div id="cp7">406,110</div></td>
                <td class="data_name">Births today</td></tr>
            <tr><td class="counter"><div id="cp8">20,311,076</div></td>
                <td class="data_name">Deaths year to date</td></tr>
            <tr><td class="counter"><div id="cp9">158,235</div></td>
                <td class="data_name">Deaths today</td></tr>
            <tr><td class="counter"><div id="cp10">0</div></td>
                <td class="data_name">Net migration year to date</td></tr>
            <tr><td class="counter"><div id="cp11">0</div></td>
                <td class="data_name">Net migration today</td></tr>
            <tr><td class="counter"><div id="cp12">31,817,362</div></td>
                <td class="data_name">Population growth year to date</td></tr>
            <tr><td class="counter"><div id="cp13">247,875</div></td>
                <td class="data_name">Population growth today</td></tr>
        </tbody></table>

I need to set an interval and the number will be counting automatically. Such as one second. How can I do that? I want to use this in my WordPress blog.

Solution

Let's assume that you have a count function. In that case, you can execute that function once per second with

setInterval(count, 1000);

Now, you need to define count, like this:

function count() {
    var items = document.querySelectorAll(".counter > div");
    for (let item of items) item.innerText = (parseInt(item.innerText.replace(/,/g, '')) - 1).toString().replace(/\B(?=(\d{3})+(?!\d))/g, ",");
}

EDIT

If you want to do them in separate intervals, then you can do something of the like

function count(item) {
    item.innerText = (parseInt(item.innerText.replace(/,/g, '')) - 1).toString().replace(/\B(?=(\d{3})+(?!\d))/g, ",");
}

and then

setInterval(function() {
    count(document.getElementById("cp1"));
}, 1000);

setInterval(function() {
    count(document.getElementById("cp2"));
}, 6000);

You can of course use your own logic to define times, the code above is just an illustration.