@loopback/docs/site/apidocs/core.mixintarget.md

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---
lang: en
title: 'API docs: core.mixintarget'
keywords: LoopBack 4.0, LoopBack 4, Node.js, TypeScript, OpenAPI
sidebar: lb4_sidebar
editurl: https://github.com/loopbackio/loopback-next/tree/master/packages/core
permalink: /doc/en/lb4/apidocs.core.mixintarget.html
---

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[Home](./index.md) &gt; [@loopback/core](./core.md) &gt; [MixinTarget](./core.mixintarget.md)

## MixinTarget type

A replacement for `typeof Target` to be used in mixin class definitions. This is a workaround for TypeScript limitation described in - https://github.com/microsoft/TypeScript/issues/17293 - https://github.com/microsoft/TypeScript/issues/17744 - https://github.com/microsoft/TypeScript/issues/36060

<b>Signature:</b>

```typescript
export declare type MixinTarget<T extends object> = Constructor<{
    [P in keyof T]: T[P];
}>;
```
<b>References:</b> [Constructor](./context.constructor.md)

## Example


```ts
export function MyMixin<T extends MixinTarget<Application>>(superClass: T) {
  return class extends superClass {
    // contribute new class members
  }
};
```
TypeScript does not allow class mixins to access protected members from the base class. You can use the following approach as a workaround:

```ts
// eslint-disable-next-line @typescript-eslint/ban-ts-comment
// @ts-ignore
(this as unknown as {YourBaseClass}).protectedMember
```
The directive `@ts-ignore` suppresses compiler error about accessing a protected member from outside. Unfortunately, it also disables other compile-time checks (e.g. to verify that a protected method was invoked with correct arguments, and so on). This is the same behavior you would get by using `Constructor<any>` instead of `MixinTarget<Application>`<!-- -->. The major improvement is that TypeScript can still infer the return type of the protected member, therefore `any` is NOT introduced to subsequent code.

TypeScript also does not allow mixin class to overwrite a method inherited from a mapped type, see https://github.com/microsoft/TypeScript/issues/38496 As a workaround, use `@ts-ignore` to disable the error.

```ts
export function RepositoryMixin<T extends MixinTarget<Application>>(
superClass: T,
) {
  return class extends superClass {
   // @ts-ignore
   public component<C extends Component = Component>(
     componentCtor: Constructor<C>,
     nameOrOptions?: string | BindingFromClassOptions,
   ) {
     const binding = super.component(componentCtor, nameOrOptions);
     // ...
     return binding;
   }
}
```