@typescript-eslint/eslint-plugin/docs/rules/no-mixed-enums.mdx

TypeScript plugin for ESLint

---
description: 'Disallow enums from having both number and string members.'
---

import Tabs from '@theme/Tabs';
import TabItem from '@theme/TabItem';

> 🛑 This file is source code, not the primary documentation location! 🛑
>
> See **https://typescript-eslint.io/rules/no-mixed-enums** for documentation.

TypeScript enums are allowed to assign numeric or string values to their members.
Most enums contain either all numbers or all strings, but in theory you can mix-and-match within the same enum.
Mixing enum member types is generally considered confusing and a bad practice.

## Examples

<Tabs>
<TabItem value="❌ Incorrect">

```ts
enum Status {
  Unknown,
  Closed = 1,
  Open = 'open',
}
```

</TabItem>
<TabItem value="✅ Correct (Explicit Numbers)">

```ts
enum Status {
  Unknown = 0,
  Closed = 1,
  Open = 2,
}
```

</TabItem>
<TabItem value="✅ Correct (Implicit Numbers)">

```ts
enum Status {
  Unknown,
  Closed,
  Open,
}
```

</TabItem>
<TabItem value="✅ Correct (Strings)">

```ts
enum Status {
  Unknown = 'unknown',
  Closed = 'closed',
  Open = 'open',
}
```

</TabItem>
</Tabs>

## Iteration Pitfalls of Mixed Enum Member Values

Enum values may be iterated over using `Object.entries`/`Object.keys`/`Object.values`.

If all enum members are strings, the number of items will match the number of enum members:

```ts
enum Status {
  Closed = 'closed',
  Open = 'open',
}

// ['closed', 'open']
Object.values(Status);
```

But if the enum contains members that are initialized with numbers -including implicitly initialized numbers— then iteration over that enum will include those numbers as well:

```ts
enum Status {
  Unknown,
  Closed = 1,
  Open = 'open',
}

// ["Unknown", "Closed", 0, 1, "open"]
Object.values(Status);
```

## When Not To Use It

If you don't mind the confusion of mixed enum member values and don't iterate over enums, you can safely disable this rule.