<script>

        var user = document.getElementById("user");

        var pwd = document.getElementById("pwd");

        var user_erro = document.getElementById("user_erro");

        var pwd_erro = document.getElementById("pwd_erro");

        //focus 获得焦点

        user.addEventListener("blur", function () {

            check_length(user); //传递参数

        }, false);

        pwd.addEventListener("blur", function () {

            check_length(pwd);

        }, false);

        function check_length(obj) {

            var that = obj;

            if (that.value.length < 1) {

                that.style.borderColor = 'rgb(255, 76, 82)'; //为空

                show_dom(that.id,"block");

            } else {

                that.style.borderColor = 'rgb(17, 194, 109)'; //不为空

                show_dom(that.id,"none");

            }

        }

        function show_dom(obj,disp) {

            switch (obj) {

                case "user":

                    user_erro.style.display = disp;

                    break;

                case "pwd":

                    pwd_erro.style.display = disp;

                    break;

            }

        }

    </script>