DOM = Document Object Model.
DOM gives us a similar model of the HTML document so that we can change the document structure, style and content.

5 way I can select HTML elements using DOM.
getElementsByTagName()
getElementsByClassName()
getElementById()
querySelector()
querySelectorAll()

Event bubble is propagating an event from the lowest to the upward.

Callback function means calling another function inside a function as a parameter.
I use it When I want one function to execute only after another function has completed its execution, means
when i need to run another function right after completing a function