Enrich user data with required fields

Issue

I often have the situation that I want to make a specific entry selectable from a set of data in a component (e.g. via select-box or as an entry in a table).

The way I want to use the data, however, often requires additional fields such as the "label: string" field in the case of a select box. In order for this to succeed, I usually enrich the user data with the required fields. For this I either write my own type (e.g. "ItemWithLabel") or implement this inline (Item & {label:string}) as shown in the example below:

@Component({
    template: '
        <my-select-component [data]="items$ | async">
        </my-select-component>
    '
})
export class MyComponent {
    items$: Observable<(Item & {label:string})[]>

    constructor(private myDataService: MyDataService) {
        this.items$ = this.myDataService.getItems()
        .pipe(
            // map the data to ensure it fits (Item & {label:string})[]
        );
    }

}

Now this seems to me to be not very clean or very complex. Is there a simpler/more elegant way of doing this?

Solution

Seems like a good use case for a generic type:

type Labelled<T> = T & { label: string };

items$: Observable<Labelled<Item>>[]>

No need to declare a new type every time.

Or if you want to keep the original data separate:

type Labelled<T> = {
  data: T;
  label: string;
};

Answered By - Chris Hamilton