How to add a custom js script in suitecrm-8?

Thanks for answering. The purpose of including this custom script is to try to apply custom validations on some fields. I plan to interact with the DOM in order to achieve this goal. Specifically to handle this scenario

https://community.suitecrm.com/t/how-can-i-add-custom-validation-to-a-custom-field-in-suitecrm-8/91723?u=mario.martinez