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

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[Home](./index.md) &gt; [@loopback/metadata](./metadata.md) &gt; [DecoratorFactory](./metadata.decoratorfactory.md) &gt; [duplicateDecorationError](./metadata.decoratorfactory.duplicatedecorationerror.md)

## DecoratorFactory.duplicateDecorationError() method

Create an error to report if the decorator is applied to the target more than once

**Signature:**

```typescript
protected duplicateDecorationError(target: Object, member?: string | symbol, descriptorOrIndex?: TypedPropertyDescriptor<any> | number): Error;
```

## Parameters

<table><thead><tr><th>

Parameter


</th><th>

Type


</th><th>

Description


</th></tr></thead>
<tbody><tr><td markdown="1">

target


</td><td markdown="1">

Object


</td><td markdown="1">

Decoration target


</td></tr>
<tr><td markdown="1">

member


</td><td markdown="1">

string \| symbol


</td><td markdown="1">

_(Optional)_ Optional property or method


</td></tr>
<tr><td markdown="1">

descriptorOrIndex


</td><td markdown="1">

TypedPropertyDescriptor&lt;any&gt; \| number


</td><td markdown="1">

_(Optional)_ Optional parameter index or method descriptor


</td></tr>
</tbody></table>

**Returns:**

Error