html js 表单提交前检测数据

 function check() {
                    var newPwd = document.getElementById("newPwd");
                    var confirmNewPwd = document.getElementById("confirmNewPwd");
                    if (newPwd.value == confirmNewPwd.value)
                        return true;
                    else {
                        var err = document.getElementById("errMSG");
                        err.style.display = "";
                        return false;
                    }

                }

<form  action="/student/UpdatePwd" onsubmit="return check()">
                <div class="control-group">
                    <label class="control-label" for="basicinput">旧密码</label>
                    <div class="controls">
                        <input placeholder="请输入…" data-original-title="" class="span8 tip" type="password" name="oldPwd" id="oldPwd">
                    </div>
                </div>
                <div class="control-group">
                    <label class="control-label" for="basicinput">新密码</label>
                    <div class="controls">
                        <input placeholder="请输入…" data-original-title="" class="span8 tip" type="password" name="newPwd" id="newPwd">
                        <span class="help-inline" style="color:red;display:none" id="errMSG">两次密码不一致</span>
                    </div>
                </div>
                <div class="control-group">
                    <label class="control-label" for="basicinput">再次输入新密码</label>
                    <div class="controls">
                        <input placeholder="请输入…" data-original-title="" class="span8 tip" type="password" id="confirmNewPwd">
                    </div>
                </div>

                <div class="control-group">
                    <div class="controls ">
                        <button type="submit" class="btn-inverse btn-large">更新</button>
                    </div>
                </div>
            </form>