设置：

function setCookie(c_name, value, expiredays) {
  var exdate = new Date();
  exdate.setTime(Number(exdate) + expiredays);
  document.cookie = c_name + "=" + escape(value) ;
}

获取:

function getCookie(c_name) {
  if(document.cookie.length > 0) {
    c_start = document.cookie.indexOf(c_name + "=");//获取字符串的起点
    if(c_start != -1) {
      c_start = c_start + c_name.length + 1;//获取值的起点
      c_end = document.cookie.indexOf(";", c_start);//获取结尾处
      if(c_end == -1) c_end = document.cookie.length;//如果是最后一个，结尾就是cookie字符串的结尾
      return decodeURI(document.cookie.substring(c_start, c_end));//截取字符串返回
    }
  }
  return "";
}

示例：

var userName =  getCookie("user_name");
console.log(userName)