Watch a specified directory's JavaScript files and recompile a specified output file if any changes are detected

uglify-watch.js

/**
 * Sample usage - note that the trailing slash on the watch directory is important!
 *
 * node uglify.js /path/to/my/src/directory/ /path/to/my/output/file.js
 */

var jsp = require('uglify-js').parser,
    pro = require('uglify-js').uglify,
    fs  = require('fs');

// take the directory to watch...
var srcDir   = process.argv[2];

// ... and the destination file as command line arguments
var destFile = process.argv[3];

// grab the files to watch...
var sourceFiles = fs.readdirSync(srcDir);

// keep a cache of compiled files so we don't have to recompile all of them every time
var compressedFiles = {};

var compile = function(file, cb) {
    var code = fs.readFileSync(file, "utf8");

    if (compressedFiles[file] == null) {
        console.log("compressing "+file);
    } else {
        console.log("re-compressing "+file);
    }

    // lifted from https://github.com/mishoo/UglifyJS
    var ast = jsp.parse(code); // parse code and get the initial AST
    ast = pro.ast_mangle(ast); // get a new AST with mangled names
    ast = pro.ast_squeeze(ast); // get an AST with compression optimizations
    var final_code = pro.gen_code(ast); // compressed code here

    // cache the compressed version of this file
    compressedFiles[file] = final_code;

    // if we've got a callback, assume it wants the output of all our files
    if (typeof cb == 'function') {
        var output = "";
        for (var i in compressedFiles) {
            output += compressedFiles[i]+";";
        }
        cb(output);
    }
}

/**
 * Go! 
 */
sourceFiles.forEach(function(file) {
    if (file.match(/\.js$/)) {

        var fullPath = srcDir+file;
        compile(fullPath);

        fs.watchFile(fullPath, function(curr, prev) {
            if (curr.mtime > prev.mtime) {
                console.log(file+" modified!");

                compile(fullPath, function(output) {
                    fs.writeFile(destFile, output, function(err) {
                        if (err) throw err;
                        console.log("written file to "+destFile);
                    });
                });
            } else {
                console.log(file+" accessed...");
            }
        });
    }
});