<igx-drop-down-item [id] = 'igx-drop-down-item-0'></igx-drop-down-item>

let itemId =  this.item.id;

// get
 let mySelectedItem = this.dropdown.selectedItem;
 let isMyItemHeader = mySelectedItem.isHeader;

<!--set-->
 <igx-drop-down-item *ngFor="let item of items">
     <div *ngIf="items.indexOf(item) === 5; then item.isHeader = true">
         {{item.field}}
     </div>
 </igx-drop-down-item>

<igx-drop-down-item [role]="customRole"></igx-drop-down-item>

// usage in IgxDropDownItemComponent
// get
let mySelectedItemValue = this.dropdown.selectedItem.value;

// set
let mySelectedItem = this.dropdown.selectedItem;
mySelectedItem.value = { id: 123, name: 'Example Name' }

// usage in IgxComboItemComponent
// get
let myComboItemValue = this.combo.items[0].value;