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README.md

JQuery

Objectives
Learn what JQuery is
See how we might integrate JQuery into our website
Apply examples of JQuery in Bootstrap

What is the DOM?

DOM stands for Document Object Model. It's a fancy way of describing what's going on in your browser when you visit a website. You may think a webpage is just a chunk of HTML, CSS, and JavaScript code. But, there's an important step between a webpage being pure data (text) and being a rendered page users can explore. Everything you interact with in the browser can be represented as a JavaScript object. For example, this paragraph is an object, and it's full of information about being an HTML <p> tag.

DOM Analogy: The Human Body

  • HTML = Skeleton
  • Javascript = Muscles, Brain, and Organs
  • CSS = Skin and Clothing

muscles

Intro to jQuery

jQuery is a powerful, easy-to-use JavaScript library. It was invented in 2005 and has made our lives as developers better ever since. The slogan for jQuery is "write less, do more". jQuery is a great toolbox that provides convenient functions we can use as opposed to writing the functionality we need from scratch.

We use jQuery because it's:

  • Convenient: solves problems developers commonly face.
  • Less Buggy: ensures JavaScript DOM manipulation works the same, cross-browser.
  • Modern: brings JavaScript DOM manipulation into the 21st century.
  • Popular: 26.95% of all sites use jQuery!

jQuery vs. Vanilla JS

It's important to note that any DOM manipulation done with jQuery can also be done with pure (vanilla) JavaScript. Some argue you might not need jQuery. It can be overkill, depending on what you're doing.

Here are some of the basic differences:

Selecting Elements

// jquery
var $divs = $('div');

// vanilla js
var divs = document.querySelectorAll('div');

Selecting Elements by Class

// jquery
var $content = $('.content');

// vanilla js
var content = document.getElementsByClassName('content');

Selecting Elements by Id

// jquery
var $about = $('#about');

// vanilla js
var about = document.getElementById('about');

Creating Elements

// jquery
var $newDiv = $('<div></div>');
$('body').append($newDiv);

// vanilla js
var newDiv = document.createElement('div');
document.body.appendChild(newDiv);

Including jQuery

To use jQuery, you must include the library in your page. The quickest way to include jQuery in your project is to copy the link to the CDN (content delivery network) and put it into a script tag at the bottom of your HTML <body>. You can get the CDN by searching for "jQuery" on cdnjs.

Important: Your JavaScript file MUST come after jQuery in the order you require scripts. This is because the page loads in order, so the jQuery library must be loaded before you can use any of it's functionality.

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
</head>
<body>
  <!-- html code here -->

  <!-- jquery -->
  <script type="text/javascript" src="https://code.jquery.com/jquery-1.11.3.min.js"></script>

  <!-- custom script -->
  <script type="text/javascript" src="main.js"></script>
</body>
</html>

Sites like GitHub, CSS-Tricks, and jquery.com (!) all include the jQuery library on their page. This means all you have to do is open up the Chrome Developer Console on one of those sites, and you can start experimenting with jQuery on the page.

Challenges

Draw a Tree

  1. Draw the structure of the following HTML document:
<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>My Site</title>
</head>
<body>
  <div class="header">
    <ul>
      <li><a href="/">Home</a></li>
      <li><a href="/about">About</a></li>
      <li><a href="/contact">Contact</a></li>
    </ul>
  </div>

  <div class="section">
    <h1>Welcome to my site!</h1>
    <img src="say-cheese.jpg">
    <p>Words and <a href="/">links</a></p>
  </div>

  <div class="footer">
    <small>Copyright 2015 Jon Doe.</small>
  </div>
</body>
</html>
  • How many children does the <div> with class header have?
  • What is the direct child of the <p> element?
  • What is the direct parent of the <p> element?

CSS Selectors

For the following code blocks, come up with as many CSS selectors as you can think of to select the HTML elements in red, and only the elements in red.

Code Block #1:

Code Block #2:

Code Block #3:

Code Block #4:

Code Block #5:

jQuery Selectors

  1. Use jQuery to select the element containing the words "Hello There" with as many different selectors as you can think of:
<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>Example 1</title>
</head>
<body>
  <div id="greeting">Hello There</div>
</body>
</html>
  1. How would you get the value "Hello There"?
  2. How would you change (or set) the value to "Hola"?
  3. How would you add an <h1> to the page that says "A Spanish Greeting"?
  4. How would you add a second greeting ("Que tal?") below the first?
  5. How would you add the class "section" to both greetings?

Where we are going next:

Thus far you have a blog with style, routes, models, and views. This will help you better understand what is happening with your page as a user interacts with it. In our next lesson we'll be using RSpec for testing the functionality of our app. This will allow us to know what parts of our application are working and know that they are working correctly.