PrimeNG goes beyond the normal checkbox behavior of the "true/false" selection on the web. In some cases, there is a need for a "true/false/null" combination, especially to represent the status of any entity. Remember that the model property is assigned to any type instead of a boolean type. A basic example of a TriStateCheckbox used to enter the feedback for Angular 4 would be as follows:

<p-triStateCheckbox name="tristate" [(ngModel)]="status">
</p-triStateCheckbox>

TriStateCheckbox will be displayed with three different states (excellent, good, and bad) as shown in the following screenshot:

This enhanced checkbox also provides the onChange event callback for any user interactions. The user actions are disabled through the disabled property, just like the normal boolean checkbox.