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

1) uglify.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...");
            }
        });
    }
});

2) Sample output

nick@nick-desktop:~/www/foo/node$ node uglify.js ~/www/foo/src/js/ ~/www/foo/public/js/run.js 
compressing /home/nick/www/foo/src/js/client.js
compressing /home/nick/www/foo/src/js/bullet.js
compressing /home/nick/www/foo/src/js/surface.js
compressing /home/nick/www/foo/src/js/input.js
compressing /home/nick/www/foo/src/js/message_box.js
client.js accessed...
client.js modified!
re-compressing /home/nick/www/foo/src/js/client.js
written file to /home/nick/www/foo/public/js/run.js

Nice idea. I started something like that for a contracting gig a while back with @JamieMason with testing a bunch of files using Guard. Also wrote Processr which helps manipulate text with filters etc. It's not Node, but I'm tempted by it with the amount of JS I'm writing lately.