how to define a type to check that an object contains an id key?

Question

Is there a way to define an interface so that it can contain any number of keys but must contain the id key?

interface HasId{
   id: number
}

Something like this can be defined but it will output an error if there is another key in the data structure.

Answer 1

Yes, in fact you need to create a dictionary type. More info on Advanced Types.

interface HasId {
    id: number;
    [key: string]: any;
}

You can also make it more generic like

interface IDictionary<T> {
    [key: string]: T;
}

interface HasId extends IDictionary<number> {
    id: number;
}