I am trying to figure out the best way to implement cross field validation in Angular. For example, I have a select field that makes another field mandatory. I want to be able to: Change the border color of the field if it is invalid Display a * in front of the field whenever it becomes mandatory Display a specific error message that explains what validation rule is broken. So far, I came up with three solutions but they don't feel so convincing to me. Listen to select field changes and update second field's validators. Listen to both fields changes and manually perform setErrors Lift validation to formGroup (which can feel extremely cumbersome since, validation state is now stored in formGroup and not directly available in formControl). Here is a Stackblitz implementation that demos my investigations. Continue reading...
