记住密码怎么做js

function check ()
{

//获取表单输入:用户名,密码,是否保存密码
var username = document.getElementById("username").value.trim() ;
var password = document.getElementById("password").value.trim() ;
var isRmbPwd = document.getElementById("isRmbPwd").checked ;

//判断用户名,密码是否为空(全空格也算空)
if ( username.length != 0 && password.length != 0 )
{
    //若复选框勾选,则添加Cookie,记录密码
    if ( isRmbPwd == true )
    {   
        setCookie ( "This is username", username, 7 ) ;
        setCookie ( username, password, 7 ) ;
    }
    //否则清除Cookie
    else
    {
        delCookie ( "This is username" ) ;
        delCookie ( username ) ;
    }
    return true ;
}
//非法输入提示
else
{
    alert('请输入必填字段!!!')
    return false ;
}   

}