
The ngModel directive updates the form control with special Angular CSS classes to reflect it's state. Let's find the list of classes in a tabular format,

| Form control state | If true    | If false     |
| ------------------ | ---------- | ------------ |
| Visited            | ng-touched | ng-untouched |
| Value has changed  | ng-dirty   | ng-pristine  |
| Value is valid     | ng-valid   | ng-invalid   |

What are the state CSS classes provided by ngModel?

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The ngIf and hidden properties in Angular control element visibility in different ways.

Form control state	If true	If false
Visited	ng-touched	ng-untouched
Value has changed	ng-dirty	ng-pristine
Value is valid	ng-valid	ng-invalid