Sometimes I need to get elements like this:
var object = document.getElementById('ObjectName');
And sometimes like this:
var object = document.getElementById('#ObjectName');
What’s the difference between them?
No, you don't see
var object = document.getElementById('#ObjectName');
You don't see that because that would mean the id of the element starts with #
and HTML4 id could only start "with a letter ([A-Za-z])".
What you see is sometimes people using the jQuery library in which the query language allows you to find an object using
var elem = $('#objectId');
And in the future you'll see more and more people using a similar query language with querySelector or querySelectorAll.