It checked that username match alpha regex or not
If you want to apply conditional validation on 'Contact Number' or 'Age', then you need to add 'userName' input as 'Bharat
{{userFormGroup.controls.userName.errors.onlyAlpha.message}}
It checked that age match with digit regex or not and it conditionaly applied when userName is Bharat
Conditional Expression with type 'string'
{{userFormGroup.controls.age.errors.onlyDigit.message}}
If you want to apply conditional validation on 'Number' then you need to add 'UserName' input as 'Bharat'.
Conditional Expression with type 'function'
{{userFormGroup.controls.contactNumber.errors.onlyDigit.message}}