jquery ajax给外部变量赋值 async: false

开发过程中用到检查是否存在手机号问题。

//验证手机号是否注册
            var bl = false;
            $.ajax({
                type: "post",
                async: false,//改为同步即可对外部变量赋值
                url: "ajax.ashx?isreg=1&tel=" + $("#tbtel").val(),
                success: function (data) {
                   
                      if (data == "1") {
                            bl = true;
                          layer.alert('该手机号已经注册！', { skin: 'layui-layer-molv', icon: 6 });
                          
                    }
                }
            })
            if (bl == true)
                return;