并不那么严谨的localStorage对象的实现(能与旧的浏览器良好兼容，如Internet Explorer < 8 (甚至能在 Internet Explorer 6 上正常工作))

if (!window.localStorage) {
  window.localStorage = {
    getItem: function (sKey) {
      if (!sKey || !this.hasOwnProperty(sKey)) { return null; }
      return unescape(document.cookie.replace(new RegExp("(?:^|.*;\\s*)" + escape(sKey).replace(/[\-\.\+\*]/g, "\\$&") + "\\s*\\=\\s*((?:[^;](?!;))*[^;]?).*"), "$1"));
    },
    key: function (nKeyId) {
      return unescape(document.cookie.replace(/\s*\=(?:.(?!;))*$/, "").split(/\s*\=(?:[^;](?!;))*[^;]?;\s*/)[nKeyId]);
    },
    setItem: function (sKey, sValue) {
      if(!sKey) { return; }
      document.cookie = escape(sKey) + "=" + escape(sValue) + "; expires=Tue, 19 Jan 2038 03:14:07 GMT; path=/";
      this.length = document.cookie.match(/\=/g).length;
    },
    length: 0,
    removeItem: function (sKey) {
      if (!sKey || !this.hasOwnProperty(sKey)) { return; }
      document.cookie = escape(sKey) + "=; expires=Thu, 01 Jan 1970 00:00:00 GMT; path=/";
      this.length--;
    },
    hasOwnProperty: function (sKey) {
      return (new RegExp("(?:^|;\\s*)" + escape(sKey).replace(/[\-\.\+\*]/g, "\\$&") + "\\s*\\=")).test(document.cookie);
    }
  };
  window.localStorage.length = (document.cookie.match(/\=/g) || window.localStorage).length

原文
https://developer.mozilla.org/zh-CN/docs/Web/API/Storage/LocalStorage