写一段js代码，完成字段校验规则：必须包含大小写字母和数字。

var regex = new RegExp("^(?=.[a-z])(?=.[A-Z])(?=.*[0-9]).{8,}$"); if(regex.test(yourString)){ console.log('The string is valid.'); } else { console.log('The string is not valid.'); }