根据 UserAgent 做页面跳转

(function(window, undefined) {
  'use strict';

  var keywords = [
    'iPod', 'iPhone', 'Android', 'Opera Mini',
    'BlackBerry', 'webOS', 'UCWEB', 'Blazer',
    'PSP', 'IEMobile', 'Symbian'
  ].join('|');
  var pa = new RegExp(keywords, 'g');

  if ( pa.test(window.navigator) ) {
    window.location.href = 'http://m.example.com';
  }
})(window);