Uncaught TypeError: Cannot read property 'innerHTML' of null

Question

Keep getting this error, no idea why

Uncaught TypeError: Cannot read property 'innerHTML' of null

My code is:

function write(message) {
  document.getElementById('message').innerHTML += message + '<br/>';
}

function calculateCircumference (diameter) {
    return diameter * 3.14;
}

write (calculateCircumference(4));

Answer 1

Admittedly, the error message is not exactly transparent as to its meaning (but at least you get an error - jQuery would just silently do nothing!)

What it means is that the result of document.getElementById('message') is null. Looking at the docs you will find that this happens when the element cannot be found.

The main reason for an element not being found is because it doesn't exist yet.

<script>// do something with document.getElementById('message');</script>
<div id="message"></div>

The above will FAIL because message does not exist yet. Moving the script after the div will make it work.

Side-note: 3.14 is far too inaccurate. Use Math.PI instead, it's as accurate as a number in JavaScript can be.

Answer 2

Seems that your code is executed before the DOM is ready

window.onload = function(){
    function write(message) {
        document.getElementById('message').innerHTML += message + '<br/>';
    }

   function calculateCircumference (diameter) {
        return diameter * 3.14;
    }

    write (calculateCircumference(4));
}

Answer 3

If you have your id is set and you still get the same error, make sure you have done the opening and closing tags of your html correctly.