# Generic type variables

## `Errors<`<mark style="color:green;background-color:green;">`Id`</mark>`>`

#### <mark style="color:green;">`Id`</mark>`extends`[<mark style="color:green;">`string`</mark>](https://www.typescriptlang.org/docs/handbook/basic-types.html#string)

​A generic type variable constrained by the [`string`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String), by default of the value **captured** from the provided rest parameter [`id`](https://docs.angular-package.dev/error/constructor#...id-id) indicates the identification type of a new [`Errors`](https://docs.angular-package.dev/error/errors) instance.

{% code title="errors.class.ts" %}

```typescript
class Errors<
  Id extends string // <--- Declare generic type variable Id.
> extends CommonErrors<Id> {
  constructor(
    ...id: Id[] // <--- Capture generic type variable Id.
  ) {
    super(...id);
  }
}
```

{% endcode %}


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