According to angular 6+,
- valid: This property returns true if the element’s contents are valid and false otherwise.
- invalid: This property returns true if the element’s contents are invalid and false otherwise.
= pristine: This property returns true if the element’s contents have not been changed.
- dirty: This property returns true if the element’s contents have been changed.
- untouched: This property returns true if the user has not visited the element.
- touched: This property returns true if the user has visited the element.