求教大神关于gruntjs的问题！

require('time-grunt')(grunt);
grunt.event.on('watch', function(action, filepath, target) {
grunt.log.writeln(target + ': ' + filepath + ' has ' + action);
});

大神们，帮忙解释下上面两句话的意思，谢谢啦

http://www.open-open.com/lib/view/open1409797661057.html