# @typescript-eslint/unbound-method

> Disallow taking a method off its object without binding it

A method gets its `this` from how it's called. If you store `user.greet` in a variable or pass it as a callback, it's later called without the object, so `this` is `undefined` and the first `this.name` throws.

Calling the method, comparing it, testing it in a condition, and `typeof` are fine. So are properties that hold an arrow function, methods declared with `this: void`, and built-in functions that don't use `this`, such as `console.log`, `Math.max`, and `JSON.parse`.

`bun lint --type-aware` turns this rule on in TypeScript files.

{/* Generated by src/codegen/lint-rule-docs.ts. Do not edit this section. */}

## Configure

Off by default. This rule needs types, so turning it on makes `bun lint` type check your code first.

```toml bunfig.toml
[lint.rules]
"@typescript-eslint/unbound-method" = "error" # or "warn"
```

Every option, set to its default:

```toml bunfig.toml
[lint.rules]
"@typescript-eslint/unbound-method" = ["error", {
  ignoreStatic = false,
}]
```

{/* End of the generated section. */}

## Examples

Reported:

{/* bad {"count": 3} */}
```ts
class User {
  name = "Ada";
  greet() {
    return `Hello ${this.name}`;
  }
}

const user = new User();
const greet = user.greet;
const { greet: hello } = user;
setTimeout(user.greet, 100);
```

Not reported:

{/* good */}
```ts
class User {
  name = "Ada";
  greet() {
    return `Hello ${this.name}`;
  }
  wave = () => `${this.name} waves`;
  static create(this: void) {
    return new User();
  }
}

const user = new User();
const greet = user.greet.bind(user);
setTimeout(() => user.greet(), 100);
setTimeout(user.wave, 100);
const create = User.create;
const log = console.log;
```

## Options

| Option | Default | What it does |
| --- | --- | --- |
| `ignoreStatic` | `false` | Don't check `static` methods. |

`Id.next` doesn't use `this`, but it's reported unless `ignoreStatic` is on:

{/* bad */}
```ts
class Id {
  static next() {
    return crypto.randomUUID();
  }
}

const ids = [1, 2, 3].map(Id.next);
```