---
url: /docs/guide/usage/linter/rules/unicorn/prefer-class-fields.md
---

### What it does

Prefers class field declarations over `this` assignments in constructors for static values.

### Why is this bad?

Class field declarations are more readable and less error-prone than assigning static
values to `this` in the constructor. Using class fields keeps the constructor cleaner
and makes the intent clearer.

### Examples

Examples of **incorrect** code for this rule:

```ts
class Foo {
  constructor() {
    this.bar = 1;
  }
}

class MyError extends Error {
  constructor(message: string) {
    super(message);
    this.name = "MyError";
  }
}

class Foo {
  foo = "foo";
  constructor() {
    this.foo = "bar";
  }
}
```

Examples of **correct** code for this rule:

```js
class Foo {
  bar = 1;
}

class MyError extends Error {
  name = "MyError";
}

class Foo {
  foo = "bar";
}
```

## How to use

## Version

This rule was added in v1.20.0.

## References