Selecting DOM elements
Generally speaking there are many different ways to select elements from an HTML document. We use these functions:
document.body // returns the whole body element of the html document
document.getElementById('unique') // returns the element with the id set to 'unique'
document.getElementsByTagName('H3') // returns an array with all h3 elements
document.getElementsByClassName('bigSize') // returns an array with this class elements
document.querySelector('p.intro') // CSS selector type. Returns the first element that is a p and has a class 'intro'
document.querySelectorAll('div img') // returns an array with images that lie inside a div
