How do I show extra option on checked checkbox?

Question

I've got dropdown:

<ng-select [items]="items" bindLabel="name" ngModel name="dropdown" formControlName="dropdown" required></ng-select>

Here are items:

 items = [
    {
      id: 1,
      name: 'Option 1'
    }, 
    {
      id: 2,
      name: 'Option 2'
    }, 
    {
      id: 3,
      name: 'Option 3'
    }, 
    { //extra option
      id: 4,
      name: 'Option 4'
    },
  ]

I want the extra item (option 4) to be hidden. When he user click on checkbox, the extra option shows up. How do I do that?

My checkbox:

<mat-checkbox class="example-margin" ngModel name="checkbox" formControlName="checkbox">Show hidden option!</mat-checkbox>

Thanks in advance!

Answer 1

Just add additional array itemsToShow which will be used in ng-select. Original array will be used just as a data source. Then on checkbox change assign to itemsToShow the original array or filtered one by id field (depending on the current checkbox value).

Component:

export class DemoComponent implements OnInit {
    checkbox = new FormControl(false);

    items = [
        { id: 1, name: 'Option 1' },
        { id: 2, name: 'Option 2' },
        { id: 3, name: 'Option 3' },
        { id: 4, name: 'Option 4'},
    ];

    itemsToShow = [];
    itemIdToHide = 4;

    ngOnInit(): void {
        this.itemsToShow = this.getFilteredItems([this.itemIdToHide]);

        this.checkbox.valueChanges.subscribe((checked) => {
            if (checked) {
                this.itemsToShow = [...this.items];
            } else {
                this.itemsToShow = this.getFilteredItems([this.itemIdToHide]);
            }
        });
    }

    private getFilteredItems(idsToHide: number[]): { id: number; name: string }[] {
        return this.items.filter((item) => !idsToHide.includes(item.id));
    }
}

Template:

<ng-select [items]="itemsToShow" bindLabel="name" ngModel name="dropdown" formControlName="dropdown" required></ng-select>
<mat-checkbox class="example-margin" [formControl]="checkbox">Show hidden option!</mat-checkbox>

Note, getFilteredItems() method can filter by multiple ids.