---
lang: en
title: 'API docs: core.application.assertinstates'
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.application.assertinstates.html
---

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[Home](./index.md) &gt; [@loopback/core](./core.md) &gt; [Application](./core.application.md) &gt; [assertInStates](./core.application.assertinstates.md)

## Application.assertInStates() method

Assert current state of the application to be one of the expected values

**Signature:**

```typescript
protected assertInStates(op: string, ...states: string[]): void;
```

## Parameters

|  Parameter | Type | Description |
|  --- | --- | --- |
|  op | string | The operation name, such as 'boot', 'start', or 'stop' |
|  states | string\[\] | Valid states |

**Returns:**

void