watch_log.html

<script src="http://code.jquery.com/jquery-1.8.3.min.js"></script>
<script>
var host = 'localhost';
var port = 3030;
var url = 'ws://' + host + ':' + port + '/';
var WebSocket = window.WebSocket || window.MozWebSocket;
var ws = new WebSocket(url);

$(function() {
    var logs = $('#logs');
    var log = $('.log');

    ws.onopen = function () {
        logs.prepend(url + 'へ接続しました');
    }

    ws.onmessage = function (msg) {
        var data = JSON.parse(msg.data);
        logs.prepend('<div class="log">' + data + '</div');
        $('.log', logs).fadeIn();
    }

    ws.onclose = function () {
        logs.prepend('切断しました');
    }
});
</script>

<h1>Apache-Logs Watcher</h1>
<div id="logs"></div>

watch_log.js

var fs = require('fs');
var exec = require('child_process').exec;
var WsServer = require('ws').Server;

var ws = new WsServer({port: 3030});
var file = '/usr/local/Cellar/nginx/1.2.7/logs/access.log';

ws.on('connection', function(socket) {
    fs.watch(file, function(eventName, fileName) {
        readAndSend(socket);
    });
});

function readAndSend(socket) {
    exec('tail -1 ' + file, function(err, stdout, stderr) {
        if (err) throw err;
        sendLog(socket, stdout); 
    });
}

function sendLog(socket, data) {
    if (socket.readyState === 1) 
        socket.send(JSON.stringify(data));
}