# @typescript-eslint/no-invalid-this

> Disallow `this` where its value is `undefined`

In a module, `this` is `undefined` at the top level and in a plain function that's called without an object. Reading `this.label` there throws a `TypeError`. The usual cause is a callback written with `function` inside a method. It doesn't get the method's `this`.

`this` is fine in methods, class fields, constructors, and arrow functions inside them. It's also fine in a function that declares a `this` parameter, and in a function that gets its `this` from `.bind()`, `.call()` or `.apply()`.

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

## Configure

Off by default. To turn it on:

```toml bunfig.toml
[lint.rules]
"@typescript-eslint/no-invalid-this" = "error" # or "warn"
```

Every option, set to its default:

```toml bunfig.toml
[lint.rules]
"@typescript-eslint/no-invalid-this" = ["error", {
  capIsConstructor = true,
}]
```

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

## Examples

Reported:

{/* bad */}
```ts
const button = {
  label: "Save",
  onClick() {
    setTimeout(function () {
      console.log(this.label);
    }, 100);
  },
};
```

Not reported:

{/* good */}
```ts
const button = {
  label: "Save",
  onClick() {
    setTimeout(() => {
      console.log(this.label);
    }, 100);
  },
};
```

{/* good */}
```ts
interface Button {
  label: string;
}

function describe(this: Button) {
  return this.label;
}
```

## Options

| Option | Default | What it does |
| --- | --- | --- |
| `capIsConstructor` | `true` | Treat a function with a name that starts with a capital letter as a constructor, where `this` is fine. |

{/* good */}
```ts
function Timer() {
  this.startedAt = Date.now();
}
```

{/* bad {"options": [{"capIsConstructor": false}]} */}
```ts
function Timer() {
  this.startedAt = Date.now();
}
```

## When not to use it

With `strict` or `noImplicitThis` in `tsconfig.json`, TypeScript already rejects a `this` that has no type, which covers most of these reports.