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Minifying your code

From: JavaScript Essential Training

Video: Minifying your code

If you have ever looked at the source of a web page, you might have seen some code that looks like this, all squeezed together and essentially unreadable. Now this is actually JavaScript here, but that doesn't mean somebody wrote it this way. This is the result of minification; the code has been minified. This is a process to go through some regular JavaScript and minimize it to compact it. We would first start by removing comments. Then we might rename long variable names and function names to shorter names, then get a little line breaks, and start to combine multiple statements onto one line.

Minifying your code

If you have ever looked at the source of a web page, you might have seen some code that looks like this, all squeezed together and essentially unreadable. Now this is actually JavaScript here, but that doesn't mean somebody wrote it this way. This is the result of minification; the code has been minified. This is a process to go through some regular JavaScript and minimize it to compact it. We would first start by removing comments. Then we might rename long variable names and function names to shorter names, then get a little line breaks, and start to combine multiple statements onto one line.

Now, minification is done for one reason, to decrease the size of the JavaScript. The reason that you do it is to improve page load times, because the script gets downloaded faster. The two things minification is not: This is not compiling your JavaScript into a machine code, or anything like that. It is functionally identical. It's just a smaller amount of characters. And number two, it's not intentionally scrambling it. Yes, minified code is ugly, and it's tougher to read, but that's not why we do it.

It's not for what's called obfuscation. Now the question is, how do you do this? Well, you could do it yourself obviously, but that would be very, very tedious, so there are lot of minification tools for JavaScript out there. Some of the better knowns are JSMin, the Yahoo UI Compressor, and Google Closure Compiler. Now many of these are command line tool. They are actually written in C or in Java. You can just download them and run them from the command line. Well, there are a couple that can be accessed over the web, like the Google's Closure Compiler.

Let's take a look at that one. Google's Closure Compiler can be downloaded so you have your own copy, but there's a version available on the web, at closure-compiler.appspot.com. What I really need to do is to grab some JavaScript of mine to minify. Well, I have some just sitting in my editor here. I'm just going to select all of it, jump back over into Closure Compiler, and paste it in there. So it's regular JavaScript. There is nothing particularly special about it. And I am just going to go ahead, leave all the settings as is, and hit Compile. And over here on the right-hand side I can see that it's actually shrunk it a bit. The original size was 1.12K, and the compiled one is 595 bytes.

Okay, we are not really starting off with a big file, but you can see the point of what's happening. The comments have been stripped out, some of the whitespace is gone, and it seems that we've done a little bit of tweaking here. However, we can take this a little bit further down. Over on the left-hand side I can choose to do an advanced setting for the Closure Compiler, hit Compile again, and that shrinks it down even further, to 479 bytes. Now in fact, Google's Closure Compiler is not just a strict minifier. It does have a few abilities inside it to detect code that might not be called.

So it's definitely an interesting one to run your code through, because it tries to do some optimization and not just minification here. But that's mainly what I'm interested in it for. So I could either grab this and just copy and paste it, although if you see, it's also giving me a copy of a file which I could actually just download here at the default.js link. Because the whole reason is that we as developers need the comments, we need that whitespace. We need the meaningful variable names. The browser doesn't need it in order to run it.

It's quite happy with the compacted version over here. So two things with minification: You only do this when you're happy that your script is correct, you pretty much only minifiy at the end. And two, of course, you keep a copy of the original for when you need to change it, because while you can unminify to an extent--you can get some white space back-- there is no way to get back a comment that doesn't exist anymore, or know what a renamed variable was originally called. Now as we will start to see a little later on, it's very common to find third-party JavaScript libraries available to download in both the minified format, such as here jQuery, that when it's minified and zipped, it's 31K, whereas, the regular version is 229K.

You would end up using the minified one on your site to make for a quick download, but you can always download and view the non-minified one if you want to read the code.

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This video is part of

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JavaScript Essential Training

56 video lessons · 113006 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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