Get width and height of an element

jQuery

var myImage = $('#myImage');
myImage.width(); // gets width of image
myImage.height(); // gets height of image

Javascript

var img = document.getElementById('myImage');
var imgwidth = img.style.width; // gets width of image
var imgheight = img.style.height; // gets height of image

Loop through some elements

jQuery

$('a').each(function(index, value){
      console.log($(this).attr('href')); // loops through all 'a' elements, logging their 'href'
});

Javascript

var aelements = document.getElementsByTagName("a"); // runs a selector for all 'a' tags
var aelementsl = aelements.length; // gets the amount of 'a' tags
while(aelementsl--){
	console.log(aelements[aelementsl].getAttribute('href')); // logs all the hrefs
}

Grabbing all 'a' elements on the page

jQuery

$('a'); // runs a selector for all 'a' tags

Javascript

document.getElementsByTagName("a"); // runs a selector for all 'a' tags

Showing & hiding elements

jQuery

var myElement = $('#myElement');
myElement.show(); // shows the element with id 'myElement'
myElement.hide(); // hides the element with id 'myElement'

Javascript

var myElement = document.getElementById('myElement');
myElement.style.display = "block"; // shows the element with id 'myElement'
myElement.style.display = "none"; // hides the element with id 'myElement'