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Where to write your JavaScript

From: JavaScript Essential Training

Video: Where to write your JavaScript

Before we get much further, let's talk a little bit about where our JavaScript should go. You see creating JavaScript like this, what's referred to as inline code, is okay to get us started but is not how we're going to continue. The problem with having your JavaScript mixed in with your HTML is not an issue on a tiny test page like this, but when you start creating more complex pages your code becomes fragmented. It becomes hard to edit. It becomes hard to maintain. And because you often do the same thing across dozens or hundreds of pages, you've got duplicated code and if you make any changes, you might have to make them dozens or hundreds of times.

Where to write your JavaScript

Before we get much further, let's talk a little bit about where our JavaScript should go. You see creating JavaScript like this, what's referred to as inline code, is okay to get us started but is not how we're going to continue. The problem with having your JavaScript mixed in with your HTML is not an issue on a tiny test page like this, but when you start creating more complex pages your code becomes fragmented. It becomes hard to edit. It becomes hard to maintain. And because you often do the same thing across dozens or hundreds of pages, you've got duplicated code and if you make any changes, you might have to make them dozens or hundreds of times.

So instead of having it this way, what's referred to as inline JavaScript, we're going to put our JavaScript in a separate file like you might do with CSS. It's easier to maintain, it's easier to use across multiple pages, and as you'll see, it's even easier to write this way. We simply cut our JavaScript from the HTML and put it in a separate file. Now we don't need to copy across the script tags; we keep those in the HTML page, because we need them to describe the link between our HTML page and the JavaScript. And we just use the source attribute, the SRC attribute, like you might do with say an image tag.

Now your JavaScript file is just text. It could be any file name, but by convention it ends with.js. Now right now these two files would need to be beside each other in a folder or subfolder, because the SRC, the source attribute, obeys the same rules as linking to an image or a style sheet file. This could be a relative link. It could be an absolute link. It could even be on another server. In this course, I'm going to tend to keep them in the same folder for simplicity. And then we can just squeeze up the script tag, because there is nothing inside it. Now we have a great division between our HTML and our JavaScript.

Let's talk a little bit more about the script tag itself. When reading other people's JavaScript, you're going to very often see this type attribute in your script tag. And this is saying not only this is script, but this is JavaScript. Officially, it could be a whole range of different options, and it's hearkening back to the days when we had to worry about what particular flavor of scripting language we were using. But if you leave it off, every browser will assume it's JavaScript anyway. Now yes, the type attribute is formerly required if you're fully complying to the HTML 4 or XHTML spec, but in the HTML5 spec it's officially optional and just defaults to JavaScript.

Now some code editors will add the type attribute automatically, and some others will complain if you don't have it. So it might be easier for you to leave it, but I have never encountered a single situation while leaving it off has any impact at all. So I'm in the rather large count that says these days just leave it off. And next question, where do you put the script tag? It's very common, as we've said before, to see the script tag in the head and although this will work, I'm not a big fan of this, because remember JavaScript is parsed and interpreted as soon as it's hit by the browser, and that means your JavaScript file could cause a delay in rendering the page.

And we really don't want to slow the page down. We want the browser to load the page, and then we'll have our script come along at the end. Now there might occasionally be a need to immediately load and process some JavaScript. For example, you might be using JavaScript to actually create the page content. Then okay, you want it as soon as possible. But if there is a good rule of thumb, it's to have your script tag not just in your body section, but at the very bottom just before the closing body tag. Now, if I'm linking to style sheets, I'll keep those links in the head section so that they do load immediately, but my general rule is style sheets up at the top, script files down at the bottom.

Now, later we might even have multiple script tags here to link to multiple JavaScript files, and then we could get concerned about what order they are in, but we'll cross that bridge when we get to it.

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This video is part of

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JavaScript Essential Training

56 video lessons · 99479 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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