---
url: /docs/guide/usage/linter/rules/eslint/no-unsafe-optional-chaining.md
---

### What it does

Disallow use of optional chaining in contexts where the `undefined` value is not allowed.

### Why is this bad?

The optional chaining (`?.`) expression can short-circuit with a return value of `undefined`.
Therefore, treating an evaluated optional chaining expression as a function, object, number, etc.,
can cause TypeError or unexpected results. For example:

### Examples

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

```javascript
var obj = undefined;
1 in obj?.foo; // TypeError
with (obj?.foo); // TypeError
for (bar of obj?.foo); // TypeError
bar instanceof obj?.foo; // TypeError
const { bar } = obj?.foo; // TypeError
```

## Configuration

This rule accepts a configuration object with the following properties:

### disallowArithmeticOperators

type: `boolean`

default: `false`

Disallow arithmetic operations on optional chaining expressions.
If this is true, this rule warns arithmetic operations on optional chaining expressions, which possibly result in NaN.

## How to use

## Version

This rule was added in v0.0.5.

## References