<p-dropdown #dd
  [options]="cars"
  [(ngModel)]="selectedCar"
  [style]="{'width':'100%'}"
  scrollHeight="400px"
  filter="true"
  filterBy="value,label"
  resetFilterOnHide="true"
  (onFocus)="OnFocus()"
  (keydown)="test($event)"  >
</p-dropdown>

OnFocus() {
    if(this.cars.length > this.totalNumberOfCars) {
      this.cars.shift();
    }
  }

test(event) {
    const charCode = event.keyCode;
    if(event.key === 'Enter') {
      this.selectedCar = this.cars.find(car => {
       return car.label.toLowerCase().includes(this.str.toLowerCase());
      });
      this.cars.unshift(this.selectedCar)
      this.str = '';
    } else if (event.key === 'Backspace') {
        this.str = this.str.replace(/.$/,"");
    } else if( (charCode > 64 && charCode < 91) || (charCode > 96 && charCode < 123) || charCode === 8) {
      console.log('here')
        this.str+= event.key;
      }
  }