浏览器：理解HTTP无状态与Cookie的使用

function setCookie(cname,cvalue,exdays)
{
  var d = new Date();
  d.setTime(d.getTime()+(exdays*24*60*60*1000));
  var expires = "expires="+d.toGMTString();
  document.cookie = cname + "=" + cvalue + "; " + expires;
}

function getCookie(cname)
{
  var name = cname + "=";
  var ca = document.cookie.split(';');
  for(var i=0; i<ca.length; i++) 
  {
    var c = ca[i].trim();
    if (c.indexOf(name)==0) return c.substring(name.length,c.length);
  }
  return "";
}

/*!
 * JavaScript Cookie v2.2.1
 * https://github.com/js-cookie/js-cookie
 *
 * Copyright 2006, 2015 Klaus Hartl & Fagner Brack
 * Released under the MIT license
 */
;(function (factory) {
  var registeredInModuleLoader;
  if (typeof define === 'function' && define.amd) {
    define(factory);
    registeredInModuleLoader = true;
  }
  if (typeof exports === 'object') {
    module.exports = factory();
    registeredInModuleLoader = true;
  }
  if (!registeredInModuleLoader) {
    var OldCookies = window.Cookies;
    var api = window.Cookies = factory();
    api.noConflict = function () {
      window.Cookies = OldCookies;
      return api;
    };
  }
}(function () {
  function extend () {
    var i = 0;
    var result = {};
    for (; i < arguments.length; i++) {
      var attributes = arguments[ i ];
      for (var key in attributes) {
        result[key] = attributes[key];
      }
    }
    return result;
  }
  function decode (s) {
    return s.replace(/(%[0-9A-Z]{2})+/g, decodeURIComponent);
  }
  function init (converter) {
    function api() {}
    function set (key, value, attributes) {
      if (typeof document === 'undefined') {
        return;
      }
      attributes = extend({
        path: '/'
      }, api.defaults, attributes);
      if (typeof attributes.expires === 'number') {
        attributes.expires = new Date(new Date() * 1 + attributes.expires * 864e+5);
      }
      // We're using "expires" because "max-age" is not supported by IE
      attributes.expires = attributes.expires ? attributes.expires.toUTCString() : '';
      try {
        var result = JSON.stringify(value);
        if (/^[\{\[]/.test(result)) {
          value = result;
        }
      } catch (e) {}
      value = converter.write ?
        converter.write(value, key) :
        encodeURIComponent(String(value))
          .replace(/%(23|24|26|2B|3A|3C|3E|3D|2F|3F|40|5B|5D|5E|60|7B|7D|7C)/g, decodeURIComponent);
      key = encodeURIComponent(String(key))
        .replace(/%(23|24|26|2B|5E|60|7C)/g, decodeURIComponent)
        .replace(/[\(\)]/g, escape);
      var stringifiedAttributes = '';
      for (var attributeName in attributes) {
        if (!attributes[attributeName]) {
          continue;
        }
        stringifiedAttributes += '; ' + attributeName;
        if (attributes[attributeName] === true) {
          continue;
        }
        // Considers RFC 6265 section 5.2:
        // ...
        // 3.  If the remaining unparsed-attributes contains a %x3B (";")
        //     character:
        // Consume the characters of the unparsed-attributes up to,
        // not including, the first %x3B (";") character.
        // ...
        stringifiedAttributes += '=' + attributes[attributeName].split(';')[0];
      }
      return (document.cookie = key + '=' + value + stringifiedAttributes);
    }
    function get (key, json) {
      if (typeof document === 'undefined') {
        return;
      }
      var jar = {};
      // To prevent the for loop in the first place assign an empty array
      // in case there are no cookies at all.
      var cookies = document.cookie ? document.cookie.split('; ') : [];
      var i = 0;
      for (; i < cookies.length; i++) {
        var parts = cookies[i].split('=');
        var cookie = parts.slice(1).join('=');
        if (!json && cookie.charAt(0) === '"') {
          cookie = cookie.slice(1, -1);
        }
        try {
          var name = decode(parts[0]);
          cookie = (converter.read || converter)(cookie, name) ||
            decode(cookie);
          if (json) {
            try {
              cookie = JSON.parse(cookie);
            } catch (e) {}
          }
          jar[name] = cookie;
          if (key === name) {
            break;
          }
        } catch (e) {}
      }
      return key ? jar[key] : jar;
    }
    api.set = set;
    api.get = function (key) {
      return get(key, false /* read as raw */);
    };
    api.getJSON = function (key) {
      return get(key, true /* read as json */);
    };
    api.remove = function (key, attributes) {
      set(key, '', extend(attributes, {
        expires: -1
      }));
    };
    api.defaults = {};
    api.withConverter = init;
    return api;
  }
  return init(function () {});
}));