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Sending messages to the console

From: JavaScript Essential Training

Video: Sending messages to the console

I've been using this alert box because we need some way of getting a message out of JavaScript, but it is kind of annoying, particularly if I have several of them, because it requires that I click the OK button to dismiss it. And it's certainly not going to be what we want to do much more except in real alert circumstances. But luckily, we have Firebug, and having Firebug gives us something very useful here. Instead of alert, from now on what I'm going to do when I want the same equivalent is I am going to change that to console.log, leaving everything else the same.

Sending messages to the console

I've been using this alert box because we need some way of getting a message out of JavaScript, but it is kind of annoying, particularly if I have several of them, because it requires that I click the OK button to dismiss it. And it's certainly not going to be what we want to do much more except in real alert circumstances. But luckily, we have Firebug, and having Firebug gives us something very useful here. Instead of alert, from now on what I'm going to do when I want the same equivalent is I am going to change that to console.log, leaving everything else the same.

This is all written in lowercase. As you can see, I have three statements here that all call console.log. Now if I run this one again, instead of having the alert box pop up in the page section, I'm actually getting a pop-up over here in the actual console, which is part of Firebug. Console.log is not officially part of the JavaScript language. It's an add-on that Firebug is bringing to the party, although it does work in other JavaScript debuggers like the ones you can get in Internet Explorer and Safari. Now what that does mean is that unlike an alert message, if you don't have the Firebug console open, you are not going to see it, but that's okay.

It's intended for us as writers of JavaScript; it's not for the end user. They should never see it, but we certainly want it. So we can write out a string as a message to the console. We could write out a variable like the variable I have defined just a step above, which is foo. I can write down multiple variables just by separating them with commas, and over on the left-hand side I am just going to hit the Clear button to clear the console, run this again, and I can see the output that I'm having here. Now, a log message is just a log message.

This could be a good message, could be a bad message, could be informative. We can make that behavior more apparent if we know there's an error, or we know it's informational, by changing the word log to one of four other words. We could change log to debug. Now I will just comment out the other lines right now. Clear the console on the left and run it. Not much of a difference on that one. Change debug to info. Now I get the little I icon here.

Change info to warn. Now I get the yellow and the exclamations mark. Or change console to error and run that, and we actually get the error message here. It's the same message, but different icons for them. Though note, if you do have an error, you will also now get it in the status bar as well, but for the most part we will just be doing console.log, the most straightforward way of doing this. We can do a few other things with the console, as we'll see later, like measuring performance and how long a script is taking to run, but if nothing else, console.log is going to come in immensely useful for us to understand our own code better.

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This video is part of

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JavaScript Essential Training

56 video lessons · 102070 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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