# unicorn/no-typeof-undefined

> Require comparing with `undefined` directly instead of `typeof x === "undefined"`

`typeof value === "undefined"` is a long way to write `value === undefined`. You only need `typeof` for a name that may not be declared at all, where reading it throws a `ReferenceError`. That's why a variable that isn't declared in the file isn't reported by default.

`--fix` rewrites the comparison to `=== undefined` or `!== undefined`. For a variable that isn't declared in the file, only `--fix-suggestions` does.

{/* 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]
"unicorn/no-typeof-undefined" = "error" # or "warn"
```

Every option, set to its default:

```toml bunfig.toml
[lint.rules]
"unicorn/no-typeof-undefined" = ["error", {
  checkGlobalVariables = false,
}]
```

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

## Examples

Reported:

{/* bad {"count": 2} */}
```js
function greet(name, options) {
  if (typeof name === "undefined") {
    name = "stranger";
  }
  return typeof options.loud !== "undefined";
}
```

Not reported:

{/* good */}
```js
function greet(name, options) {
  if (name === undefined) {
    name = "stranger";
  }
  return options.loud !== undefined;
}

// `window` is not declared in this file
const isServer = typeof window === "undefined";
```

## Options

| Option | Default | What it does |
| --- | --- | --- |
| `checkGlobalVariables` | `false` | Also report `typeof` on a variable that isn't declared in the file. |

{/* bad {"options": [{"checkGlobalVariables": true}]} */}
```js
const isServer = typeof window === "undefined";
```