---
url: /docs/guide/usage/linter/rules/typescript/strict-boolean-expressions.md
---

### What it does

Disallow certain types in boolean expressions.

### Why is this bad?

Forbids usage of non-boolean types in expressions where a boolean is expected.
`boolean` and `never` types are always allowed. Additional types which are
considered safe in a boolean context can be configured via options.

The following nodes are checked:

* Arguments to the `!`, `&&`, and `||` operators
* The condition in a conditional expression (`cond ? x : y`)
* Conditions for `if`, `for`, `while`, and `do-while` statements.

### Examples

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

```ts
const str = "hello";
if (str) {
  console.log("string");
}

const num = 42;
if (num) {
  console.log("number");
}

const obj = { foo: "bar" };
if (obj) {
  console.log("object");
}

declare const maybeString: string | undefined;
if (maybeString) {
  console.log(maybeString);
}

const result = str && num;
const ternary = str ? "yes" : "no";
```

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

```ts
const str = "hello";
if (str !== "") {
  console.log("string");
}

const num = 42;
if (num !== 0) {
  console.log("number");
}

const obj = { foo: "bar" };
if (obj !== null) {
  console.log("object");
}

declare const maybeString: string | undefined;
if (maybeString !== undefined) {
  console.log(maybeString);
}

const bool = true;
if (bool) {
  console.log("boolean");
}
```

## Configuration

This rule accepts a configuration object with the following properties:

### allowAny

type: `boolean`

default: `false`

Whether to allow `any` type in boolean contexts.

### allowNullableBoolean

type: `boolean`

default: `false`

Whether to allow nullable boolean types (e.g., `boolean | null`) in boolean contexts.

### allowNullableEnum

type: `boolean`

default: `false`

Whether to allow nullable enum types in boolean contexts.

### allowNullableNumber

type: `boolean`

default: `false`

Whether to allow nullable number types (e.g., `number | null`) in boolean contexts.

### allowNullableObject

type: `boolean`

default: `true`

Whether to allow nullable object types in boolean contexts.

### allowNullableString

type: `boolean`

default: `false`

Whether to allow nullable string types (e.g., `string | null`) in boolean contexts.

### allowNumber

type: `boolean`

default: `true`

Whether to allow number types in boolean contexts (checks for non-zero numbers).

### allowString

type: `boolean`

default: `true`

Whether to allow string types in boolean contexts (checks for non-empty strings).

## How to use

## Version

This rule was added in v1.25.0.

## References