Easy-to-follow video tutorials help you learn software, creative, and business skills.Become a member

Using Firebug

From: JavaScript Essential Training

Video: Using Firebug

So we've been using Firefox with Firebug, although these days every modern web browser has the equivalent tools. Safari has their developer tools menu, as does Internet Explorer, as does Chrome, Opera has Dragonfly, and without exception, these days, they are all very, very good, but Firebug is certainly the best known. Now we've been mainly using it so far for the Console panel to view console messages and to type JavaScript, but it's much more useful than that. If you haven't used this already, you can use the HTML tab to actually scan and expand the HTML that you're using.

Using Firebug

So we've been using Firefox with Firebug, although these days every modern web browser has the equivalent tools. Safari has their developer tools menu, as does Internet Explorer, as does Chrome, Opera has Dragonfly, and without exception, these days, they are all very, very good, but Firebug is certainly the best known. Now we've been mainly using it so far for the Console panel to view console messages and to type JavaScript, but it's much more useful than that. If you haven't used this already, you can use the HTML tab to actually scan and expand the HTML that you're using.

If you notice that as I'm mousing over different sections here, it's actually highlighting in the top part of the page. And you can view the DOM, the actual Document Object Model of this page. I can see the document here, start to open that up, and drill down inside it. The DOM is very useful, but it can be a little intimidating at first because you'll realize there is a lot more going on with the DOM than just a few nodes. You quickly see that each node has many more properties than we could cover in this course, but you can view the properties of a particular node.

I'm looking at document right now. I can see if it has any childNodes. Yes, it does. Here is HTML, drill down into that. Does it have childNodes? Yes, it does. It has the head section with a blank line between them, which is technically a TextNode. Open the body. Does it have childNodes? Well, I'd hope so. Yes, it's got div. It's got script. It's got TextNodes itself. And you can also scan to figure out if any of these have properties that you might be interested in. Now one good thing is if you're much happier with HTML, and most people are, at least to begin with, you could drill down into your HTML, say, into the footer and into a footermenu section, find a particular place, say, such as this h3, and then use the Context menu, right-click or Ctrl+Click depending on what operating system you have, and click Inspect in DOM tab and it would drill you down directly into the particular node that you're looking at here, which if I start browsing through, I can even see that this one has childNodes.

It's got one childNode and at position zero, it's the TextNode with the contents Quick Nav inside it. Now one thing worth pointing out with this is if you are using JavaScript to change DOM content after your HTML has loaded, know that you won't see your changes if you're just used to the View Source feature of the browser. For example, I have a title up here that was actually replaced by some JavaScript--tried to make that reasonably obvious. Now if I right-click somewhere and click the option to View Page Source, which you'll get in any browser, the actual section that that originally was had the word Mission in it.

So the View Source still has the old content. This is in the h1 called pageID. However, if I'm using Firebug, either in the DOM or in the HTML, and I can drill down into the particular sections that's in mainContent here, I've got the pageID with "This title was replaced by JavaScript." So Firebug is actually giving me the more up-to-date version, which is very useful if you're starting to manipulate the DOM in JavaScript. But the panel that we'll get more and more interested in is the script part of Firebug.

That's telling me a message here that it's disabled right now. I'm going to enable it and then reload the page. And what this does is let me view all the JavaScript being used by this page, whether that's inline in the HTML, and I have a little bit here, and that was just to prove this point that some JavaScript actually in the HTML itself that it would show me. Or if I'm using a separate file, which I'm also doing, I can click on this dropdown menu here at the top, and it allows me to switch between the different files that have JavaScript in them.

That's quite common that you'll actually see several files here when you're using this dropdown. And the best thing about this panel is that it will allow us to do JavaScript debugging. We would be able to follow this code as it runs. We can set breakpoints in our code to automatically pause when we're about to hit that line, allow us to read the current values of variables, and step through the code line by line to really understand what's going on.

Show transcript

This video is part of

Image for JavaScript Essential Training
JavaScript Essential Training

56 video lessons · 102063 viewers

Simon Allardice
Author

 
Expand all | Collapse all
  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

Start learning today

Get unlimited access to all courses for just $25/month.

Become a member
Sometimes @lynda teaches me how to use a program and sometimes Lynda.com changes my life forever. @JosefShutter
@lynda lynda.com is an absolute life saver when it comes to learning todays software. Definitely recommend it! #higherlearning @Michael_Caraway
@lynda The best thing online! Your database of courses is great! To the mark and very helpful. Thanks! @ru22more
Got to create something yesterday I never thought I could do. #thanks @lynda @Ngventurella
I really do love @lynda as a learning platform. Never stop learning and developing, it’s probably our greatest gift as a species! @soundslikedavid
@lynda just subscribed to lynda.com all I can say its brilliant join now trust me @ButchSamurai
@lynda is an awesome resource. The membership is priceless if you take advantage of it. @diabetic_techie
One of the best decision I made this year. Buy a 1yr subscription to @lynda @cybercaptive
guys lynda.com (@lynda) is the best. So far I’ve learned Java, principles of OO programming, and now learning about MS project @lucasmitchell
Signed back up to @lynda dot com. I’ve missed it!! Proper geeking out right now! #timetolearn #geek @JayGodbold
Share a link to this course

What are exercise files?

Exercise files are the same files the author uses in the course. Save time by downloading the author's files instead of setting up your own files, and learn by following along with the instructor.

Can I take this course without the exercise files?

Yes! If you decide you would like the exercise files later, you can upgrade to a premium account any time.

Become a member Download sample files See plans and pricing

Please wait... please wait ...
Upgrade to get access to exercise files.

Exercise files video

How to use exercise files.

Learn by watching, listening, and doing, Exercise files are the same files the author uses in the course, so you can download them and follow along Premium memberships include access to all exercise files in the library.


Exercise files

Exercise files video

How to use exercise files.

For additional information on downloading and using exercise files, watch our instructional video or read the instructions in the FAQ.

This course includes free exercise files, so you can practice while you watch the course. To access all the exercise files in our library, become a Premium Member.

Join now "Already a member? Log in

Are you sure you want to mark all the videos in this course as unwatched?

This will not affect your course history, your reports, or your certificates of completion for this course.


Mark all as unwatched Cancel

Congratulations

You have completed JavaScript Essential Training.

Return to your organization's learning portal to continue training, or close this page.


OK
Become a member to add this course to a playlist

Join today and get unlimited access to the entire library of video courses—and create as many playlists as you like.

Get started

Already a member?

Become a member to like this course.

Join today and get unlimited access to the entire library of video courses.

Get started

Already a member?

Exercise files

Learn by watching, listening, and doing! Exercise files are the same files the author uses in the course, so you can download them and follow along. Exercise files are available with all Premium memberships. Learn more

Get started

Already a Premium member?

Exercise files video

How to use exercise files.

Ask a question

Thanks for contacting us.
You’ll hear from our Customer Service team within 24 hours.

Please enter the text shown below:

The classic layout automatically defaults to the latest Flash Player.

To choose a different player, hold the cursor over your name at the top right of any lynda.com page and choose Site preferencesfrom the dropdown menu.

Continue to classic layout Stay on new layout
Exercise files

Access exercise files from a button right under the course name.

Mark videos as unwatched

Remove icons showing you already watched videos if you want to start over.

Control your viewing experience

Make the video wide, narrow, full-screen, or pop the player out of the page into its own window.

Interactive transcripts

Click on text in the transcript to jump to that spot in the video. As the video plays, the relevant spot in the transcript will be highlighted.

Are you sure you want to delete this note?

No

Your file was successfully uploaded.

Thanks for signing up.

We’ll send you a confirmation email shortly.


Sign up and receive emails about lynda.com and our online training library:

Here’s our privacy policy with more details about how we handle your information.

Keep up with news, tips, and latest courses with emails from lynda.com.

Sign up and receive emails about lynda.com and our online training library:

Here’s our privacy policy with more details about how we handle your information.

   
submit Lightbox submit clicked
Terms and conditions of use

We've updated our terms and conditions (now called terms of service).Go
Review and accept our updated terms of service.