grunt-prepr

Grunt task that provides a C/C++ like preprocessor (with some limitations, see examples) for JavaScript, CSS and other source code. Supported directives are:

#ifdef
#ifndef
#endif
#define
#undef

The task allows to perform both conditional preprocessing of the source code and to define macros.

Getting Started

Setup task grunt-prepr with grunt.js

Install this task next to your project's grunt.js gruntfile with:

npm install grunt-prepr

Then add the line bellow to your project's grunt.js gruntfile:

grunt.loadNpmTasks('grunt-prepr');

How to config

The standard Grunt conventions are followed when configuring task:

grunt.initConfig({
  prepr: {
    //Mask, output directory specified
    target1: {
      defined: ["PROD"],
      src: "in/*.js",
      dest: "."
    },
    //Mask, outputting in the same directory
    target2: {
      defined: ["DEBUG"],
      src: "in/*.js"
    },
    //File mask, JS and CSS, output directory specified
    target3: {
      defined: ["DEBUG"],
      src: "in/*",
      dest: "."
    },
    //Processing single file
    target4: {
      src: "in/valid_styles_with_variables.css",
      dest: "."
    },
    //Processing recursively all JS files
    target5: {
      defined: ["DEBUG"],
      src: "in/**/*.js",
      dest: "."
    },
    //Preserving blank lines when directives have been processed: using option keepLineBreaks
    target6: {
      src: "in/*.js",
      dest: ".",
      keepLineBreaks: true
    }
  }
});

Using as browserify transform

browserify:     {
    options:      {
        transform:  [ require('grunt-prepr').browserify(["DEBUG"]) ],
    }
}

Examples

For more details, refer to the examples in the repository and Jasmine specs.

Although the examples below deal only with JavaScript and CSS, the preprocessor can be used for any source files.

Conditionals

Input:

function add(x, y) {
//#ifdef DEBUG
    console.log("add(" +  x + ", " + y + ")");
//#endif
    return x + y;
}

Task configuration:

grunt.initConfig({
  prepr: {
    dev: {
      defined: ["DEBUG"],
      src: "src/*.js",
      dest: "build"
    },
    prod: {
      defined: ["PROD"],
      src: "src/*.js",
      dest: "dist"
    }
  }
});

Result of running grunt prepr:prod:

function add(x, y) {
    return x + y;
}

Result of running grunt prepr:dev:

function add(x, y) {
    console.log("add(" +  x + ", " + y + ")");
    return x + y;
}

So in the development version logging to console will be left intact while in the production version it will be removed.

Defining macros

With macros we can, for example, define colors in CSS.

Input:

/* #define $COLOR1 rgb(12, 12, 12)
   #define $COLOR2 rgb(23, 45, 67)
   #define $DEFAULT_BOX_WIDTH 300px*/
.container {
    width: $DEFAULT_BOX_WIDTH;
    position: relative;
}
 
.button {
    background-color: $COLOR1;
}

Output:

.container {
    width: 300px;
    position: relative;
}
 
.button {
    background-color: rgb(12, 12, 12);
}

Macros can also take parameters, please, refer to the Jasmine specs.

Avoid abusing macros

A word of caution about using macros. The same concerns as in C/C++ apply, the preprocessor is pretty unaware of the structure of the code (unlike Lisp macros). It treats code as strings and modifications then are pretty limited, the source code with preprocessor directives may become invalid if not handled by a preprocessor and moreover the resulting code may also be invalid if the macros were defined incorrectly.

I would say that #define should not be used with JavaScript in most of the cases because of these limitations. Just use the normal functions instead. For example,

instead of:

#define MAX(X, Y) (X > Y ? X : Y)
 
MAX(3, 4);

use pure JavaScript solution:

function max(x, y) {
    return x > y ? x : y;
}
 
max(3, 4);

License

MIT License (c) Anton Ivanov

Credits

The following plugins are used during the build:

• JSHint for Grunt grunt-contrib-jshint
• Jasmine for Grunt grunt-contrib-jasmine

The task was inspired by:

• C preprocessor c-preprocessor