Question

In following code document.getElementById("clock") is null, How can it be solved?

    var interval = self.setInterval("clock()", 1000);
    function clock() {
        var date = new Date();
        var hourOffset = 3;
        date.setUTCHours(date.getUTCHours(), date.getUTCMinutes());
        var time = date.getTime();
        date.setUTCFullYear(date.getUTCFullYear(), 2, 22);
        var dstStart = date.getTime();
        date.setUTCFullYear(date.getUTCFullYear(), 8, 22);
        var dstEnd = date.getTime();
        if(time > dstStart && time < dstEnd)
            hourOffset = 4;
        date.setUTCHours(date.getUTCHours() + hourOffset, date.getUTCMinutes() + 30);
        var output = date.getUTCHours() + ":" + date.getUTCMinutes() + ":" + date.getUTCSeconds();
        document.getElementById("clock").innerHTML = output;
    }

Answer 1

First of all, you need an element with id “clock”, secondly, you need to execute that code after the DOM is ready, not before because otherwise JS won’t find the element.

In other words… add:

<div id='clock'></div>

And paste that javascript code before the </body> in your document.