Cookie的新增，设置与清除

 addCookieBtn.addEventListener('click',function () {
     document.cookie='imooc=www.imooc.com;expires=2016-07-20 10:10:10';
     content.innerHTML='cookie写入完成'
 })
 var getCookieBtn=document.getElementById('getCookieBtn');
 getCookieBtn.addEventListener('click',function (ev) {
     content.inner="Cookie获取完成：<br/>"+document.cookie;
 });
 var clearCookBtn=document.getElementById('clearCookieBtn');
 clearCookieBtn.addEventListener('click',function () {
     document.cookie="imooc=www.imo0oc.com;expires=2016-03-14 10:20:20";
     content.innerHTML="cookie清除完成"
 })