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class ApplicationController < ActionController::Base
  before_action :detect_device_variant

  private

    def detect_device_variant
      case request.user_agent
      when /iPad/i
        request.variant = :tablet
      when /iPhone/i

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<img src="abc.JPG" onerror="this.src='default.JPG'" />


或者

<script type="text/javascript">
  t = document.getElementsByClassName("defaultImg");
  for(i = 0; i < t.length; i++){
      t.item(i).onerror = function(){
        this.src = "test.gif"

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app/views/layouts/_async_javascript.html.erb

<script type="text/javascript">
  (function() {
    var script = document.createElement('script');
    script.type = 'text/javascript';
    script.async = true;
    script.src = '<%= j javascript_path(path) %>';
    var other = document.getElementsByTagName('script')[0];
    other.parentNode.insertBefore(script, other);

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#!/usr/bin/env bash

# Pre-requisites
sudo apt-get -y update
sudo apt-get -y install git-core curl autoconf automake openssl vim build-essential libc6-dev libreadline6 libreadline6-dev zlib1g zlib1g-dev libssl-dev libyaml-dev mysql-server libmysqlclient-dev ncurses-dev libtool bison libxslt1-dev libxml2-dev

# rbenv
curl https://raw.github.com/fesplugas/rbenv-installer/master/bin/rbenv-installer | bash
echo 'export PATH="$HOME/.rbenv/bin:$PATH"' >> ~/.bash_profile
echo 'eval "$(rbenv init -)"' >> ~/.bash_profile

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<style type="text/css">
<!-- 
div {
	position:absolute;
	top:50%;
	left:50%;
	margin:-150px 0 0 -200px;
	width:400px;
	height:300px;
	border:1px solid #008800;

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# coding: utf-8
#正则用于匹配用户名
str = "@wikimo @中國 @水手 测试看看"

#{2,20}字符长度至少2个，不多于20个，以下任意方式匹配
#arr = str.scan(/@([一-龠\w]{2,20}\s)/u).flatten
arr = str.scan(/@([\p{Han}+\w]{2,20}\s)/u).flatten

前端：https://github.com/ichord/jquery-atwho-rails

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Creating and Signing Your Certs
This is SSL, so you'll need an cert-key pair for you/the server, the api users/the client and a CA pair. You will be the CA in this case (usually a role played by VeriSign, thawte, GoDaddy, etc.), signing your client's certs. There are plenty of tutorials out there on creating and signing certificates, so I'll leave the details on this to someone else and just quickly show a sample here to give a complete tutorial. NOTE: This is just a quick sample of creating certs and not intended for production.

# Create the CA Key and Certificate for signing Client Certs
openssl genrsa -des3 -out ca.key 4096
openssl req -new -x509 -days 365 -key ca.key -out ca.crt

# Create the Server Key, CSR, and Certificate
openssl genrsa -des3 -out server.key 1024
openssl req -new -key server.key -out server.csr

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// Load libraries
var https = require('https');
var fs = require('fs');
var socketio = require('socket.io');

// The server options
var svrPort = 8888; // This is the port of service
var svrOptions = {
    key: fs.readFileSync('certs/server.key'),
    cert: fs.readFileSync('certs/server.crt'),

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通过json访问新浪ip数据库，可以获得相应城市的ip地址。

例行惯例，不解释：

<script type="text/javascript" >
$(document).ready(function(){
	jQuery.getScript("http://int.dpool.sina.com.cn/iplookup/iplookup.php?format=js", function(){
		alert("province : "+remote_ip_info.province+", city : "+remote_ip_info.city);
    });
});

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wget -m -p -E -k -K -np http://twitter.github.io/bootstrap/