js实现cookie写入和读取操作

var u = "value=123"; 
document.cookie = u; 

var c_name="value"; // 变量名 
if (document.cookie.length > 0) { 
  c_start = document.cookie.indexOf(c_name + "=") 
  if (c_start != -1) { 
    c_start = c_start + c_name.length + 1 
    c_end = document.cookie.indexOf(";", c_start) 
if (c_end == -1) c_end = document.cookie.length 
//  document.write(document.cookie.substring(c_start,c_end)+"<br>"); 
    var sss= unescape(document.cookie.substring(c_start, c_end))  // 取出值
    alert(sss) 
  } 
 }