Exclude debug JavaScript code during minification

Question

I'm looking into different ways to minify my JavaScript code including the regular JSMin, Packer, and YUI solutions. I'm really interested in the new Google Closure Compiler, as it looks exceptionally powerful.

I noticed that Dean Edwards packer has a feature to exclude lines of code that start with three semicolons. This is handy to exclude debug code. For instance:

;;;     console.log("Starting process");

I'm spending some time cleaning up my codebase and would like to add hints like this to easily exclude debug code. In preparation for this, I'd like to figure out if this is the best solution, or if there are other techniques.

Because I haven't chosen how to minify yet, I'd like to clean the code in a way that is compatible with whatever minifier I end up going with. So my questions are these:

1. Is using the semicolons a standard technique, or are there other ways to do it?

2. Is Packer the only solution that provides this feature?

3. Can the other solutions be adapted to work this way as well, or do they have alternative ways of accomplishing this?

4. I will probably start using Closure Compiler eventually. Is there anything I should do now that would prepare for it?

Answer 1

here's the (ultimate) answer for closure compiler :

/** @const */
var LOG = false;
...
LOG && log('hello world !'); // compiler will remove this line
...

this will even work with SIMPLE_OPTIMIZATIONS and no --define= is necessary !

Answer 2

Here's what I use with Closure Compiler. First, you need to define a DEBUG variable like this:

/** @define {boolean} */
var DEBUG = true;

It's using the JS annotation for closure, which you can read about in the documentation.

Now, whenever you want some debug-only code, just wrap it in an if statement, like so:

if (DEBUG) {
  console.log("Running in DEBUG mode");
}

When compiling your code for release, add the following your compilation command: --define='DEBUG=false' -- any code within the debug statement will be completely left out of the compiled file.