是否有带有条件指令的JavaScript缩小器？

Question

I'm looking for a JavaScript minifier which will have some kind of support for something similar to conditional compilation directives .

So for example, the original JavaScript code could look like something similar to this:

//#if Dev
    showLoginScreen();
//#else
    login("DevUser", "qwerty1");
//#endif

So the original code could contain a directive #define Dev but once it goes into production that #define Dev would be removed, and the minifier would exclude the line login("DevUser", "qwerty1"); from its output.

Do any minifiers support this kind of behavior?

Answer 1

Just run the code through the C preprocessor, then run that output through the minifier. The C preprocessor isn't really C-specific beyond its handling of string literals.

Example:

cpp -DDev file.js /dev/stdout | jsmin > file-min.js

where file.js is:

#if Dev
    showLoginScreen();
#else
    login("DevUser", "qwerty1");
#endif

will include the Dev code and then minify it.

In order to make the original source code executable as-is, you can add one more step to the processing pipeline. Write your code like this:

//#if Dev
    showLoginScreen();
//#else
    login("DevUser", "qwerty1");
//#endif

and then process it like this:

sed 's!^//#!#!' file.js | cpp -DDev /dev/stdin /dev/stdout | jsmin > file-min.js

The sed portion serves to strip the leading // from lines beginning with //# . cpp then preprocesses the source as normal, and the output from cpp is fed through jsmin for minification.

A better solution is probably just to do as C programmers do and always preprocess your source file appropriately before running. You might edit a .jspp ("pre-process JavaScript") file, and have your system set up to preprocess it appropriately for development or deployment whenever you change things. If you're using frequent testing, you can make the preprocessing part of your test tool's invocation.

(NOTE: The command line might be off; I worked out the cpp part from the manpage and the jsmin part from the jsmin.c source code file, so I haven't actually tested this command line.)

Answer 2

I looked at the C preprocessor and a few other contenders based on answers to similar questions. Then found what I think is the best answer by far - PHP. Consider:

1) PHP is indeed a preprocessor (it's in the acronym).

2) PHP is ready to go on most servers. All you have to do is either change your file extensions from ".js" to ".php" or ".js.php", or (my preference), make a simple edit to a config file (you can find the details elsewhere).

3) Many JavaScript developers are already familiar with, or expert at, PHP.

4) PHP is Turing-complete, unlike many other preprocessors.

5) You only need basic PHP knowledge to benefit a lot.

6) There is way more documentation/tutorials/forums for PHP than other preprocessors.

But mostly, it's so weird it's cool. Thanks to whoever gave me the idea - I can't find their post at the moment.