build.js

/*jslint node*/

var sass = require('sass');
var fs = require('fs');
var chokidar = require('chokidar');

// Process a scss file
function writeCSS(scssFile, cssFile) {
    'use strict';
    console.log('Rebuilding CSS from ' + scssFile);
    sass.render({
        file: scssFile,
        outFile: cssFile
    }, function (error, result) {
        if (error) {
            console.log('Error with Sass rendering:' + error);
        } else {
            fs.writeFile(cssFile, result.css, function (error) {
                if (error) {
                    console.log('Error writing the file to disk: ' + error);
                }
            });
        }
    });
}

// Build once...
writeCSS('source/main.scss', 'public/main.css');

// ...then watch for changes
var toWatch = ['source'];
chokidar.watch(toWatch, {ignored: /main\.css/}).on('all', function (event, path) {
    'use strict';
    console.log(event + ' at ' + path);
    writeCSS('source/main.scss', 'public/main.css');
});