Uncaught Typeerror: cannot read property 'innerHTML' of null

Question

Can anyone explain what is theses errors?

Uncaught TypeError: cannot read property \'innerHTML\' of null

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Answer 1

Update:

The question doesn't ask for jquery. So lets do it without jquery:

document.addEventListener("DOMContentLoaded", function(event) { 
    //Do work
});

Note this method will not work on IE8.

Old Answer:

You are calling this script before DOM is ready. If you write this code into jquery's $(function() method it will work.