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Removing and applying CSS classes

From: JavaScript Essential Training

Video: Removing and applying CSS classes

If you have a class defined in your CSS file, such as this one called.example, it's very easy to make this apply to a particular element in JavaScript; in fact, you'll spend more code saying when you want this to happen than actually doing it. If I look at some example of JavaScript, I have to apply this class called example. This is the only code that I actually need to write. Find the element, .className, =example.

Removing and applying CSS classes

If you have a class defined in your CSS file, such as this one called.example, it's very easy to make this apply to a particular element in JavaScript; in fact, you'll spend more code saying when you want this to happen than actually doing it. If I look at some example of JavaScript, I have to apply this class called example. This is the only code that I actually need to write. Find the element, .className, =example.

The only code that I'm wrapping around it here, not surprisingly, is being called when the document loads and just so I can have a bit of interactivity, I am going to respond to an onclick event on the div called mainContent. I am going to execute this anonymous function that actually asks, what is that class? Is that class currently set to example? If it is, I am going to blank it out. If it isn't, I am going to set it to example. So you've just got a little toggle on/off here happening.

If I jump over and just open that up in the browser, right now that class is not being applied, but if I click anywhere in this main div, we're applying that class, which is actually setting this part of text to white, and just clicking back and forth. It's either applying the class or taking it off. Now, one thing to note, you can apply a class all you want, but it's still using the cascading rules of CSS, which means if there are more specific rules being applied to some of this content, say through ids or even inline styles, the closer ones are going to win.

So in this case what it looks like we're doing is we are being successful in applying the color--white--to the headline, but it looks like the paragraph probably has its own color being set a little closer to it. It doesn't look like font-size is making any difference, although we do have 1em there. Text-align right certainly looks like its being applied. Again, this all comes down to normal CSS rules. JavaScript applying a class is pretty much the same as manually applying that class in your HTML when the page loads.

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This video is part of

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JavaScript Essential Training

56 video lessons · 113119 viewers

Simon Allardice
Author

 
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  1. 3m 28s
    1. Welcome
      1m 1s
    2. What you should know
      1m 44s
    3. Using the exercise files
      43s
  2. 15m 41s
    1. Introduction to JavaScript
      8m 6s
    2. Creating your first JavaScript
      2m 13s
    3. Getting to know the tools and applications
      5m 22s
  3. 56m 8s
    1. Understanding the structure of JavaScript code
      7m 9s
    2. Where to write your JavaScript
      3m 56s
    3. Creating variables
      6m 21s
    4. Working with conditional code
      5m 44s
    5. Working with operators
      13m 28s
    6. Sending messages to the console
      2m 59s
    7. Working with loops
      8m 1s
    8. Creating functions
      8m 30s
  4. 36m 13s
    1. Working with arrays
      7m 57s
    2. Working with numbers
      6m 13s
    3. Working with strings
      8m 27s
    4. Working with dates
      5m 38s
    5. Working with objects
      7m 58s
  5. 9m 6s
    1. What is the DOM?
      5m 49s
    2. Working with nodes and elements
      3m 17s
  6. 25m 17s
    1. Accessing DOM elements
      11m 3s
    2. Changing DOM elements
      5m 42s
    3. Creating DOM elements
      8m 32s
  7. 24m 45s
    1. Introduction to JavaScript event handling
      8m 16s
    2. Working with onClick and onLoad events
      7m 36s
    3. Working with onBlur and onFocus events
      2m 36s
    4. Working with timers
      6m 17s
  8. 21m 41s
    1. Common JavaScript errors
      7m 14s
    2. Using Firebug
      4m 7s
    3. Going through a debugging session
      10m 20s
  9. 10m 13s
    1. Accessing form elements
      4m 20s
    2. Preventing a form from being submitted
      2m 36s
    3. Hiding and showing form sections
      3m 17s
  10. 9m 49s
    1. CSS and JavaScript
      3m 46s
    2. Removing and applying CSS classes
      2m 16s
    3. Changing inline styles
      3m 47s
  11. 19m 44s
    1. Understanding JavaScript style
      7m 39s
    2. Minifying your code
      4m 28s
    3. Using JavaScript code checkers
      7m 37s
  12. 22m 24s
    1. Introduction to JavaScript libraries
      3m 17s
    2. Linking to multiple JavaScript files
      2m 11s
    3. Introduction to jQuery
      12m 7s
    4. Using a content distribution network to deliver JavaScript files
      4m 49s
  13. 17m 35s
    1. JavaScript in HTML5
      9m 37s
    2. Using Modernizr
      3m 2s
    3. Using Strict Mode
      4m 56s
  14. 33m 3s
    1. Knowing the JavaScript to avoid
      6m 35s
    2. Introduction to regular expressions
      6m 56s
    3. Working with AJAX
      10m 44s
    4. Working with objects and prototypes
      8m 48s
  15. 21m 10s
    1. Example: Countdown
      8m 3s
    2. Example: Resize
      5m 47s
    3. Example: Accordion
      7m 20s
  16. 4m 58s
    1. Where to go from here
      4m 0s
    2. Goodbye
      58s

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