# Source: https://oxc.rs/docs/guide/usage/linter/rules/eslint/no-unsafe-optional-chaining.md

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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

To **enable** this rule using the config file or in the CLI, you can use:

::: code-group

```json [Config (.oxlintrc.json)]
{
  "rules": {
    "no-unsafe-optional-chaining": "error"
  }
}
```

```bash [CLI]
oxlint --deny no-unsafe-optional-chaining
```

:::

## References

* Rule Source