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---
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) > [@loopback/core](./core.md) > [Application](./core.application.md) > [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
<table><thead><tr><th>
Parameter
</th><th>
Type
</th><th>
Description
</th></tr></thead>
<tbody><tr><td markdown="1">
op
</td><td markdown="1">
string
</td><td markdown="1">
The operation name, such as 'boot', 'start', or 'stop'
</td></tr>
<tr><td markdown="1">
states
</td><td markdown="1">
string\[\]
</td><td markdown="1">
Valid states
</td></tr>
</tbody></table>
**Returns:**
void