[API reference](https://evolu.dev/docs/api-reference) › [@evolu/common](https://evolu.dev/docs/api-reference/common) › [Assert](https://evolu.dev/docs/api-reference/common/Assert) › assertTrue

## Call Signature

```ts
function assertTrue(condition: boolean): asserts condition;
```

Defined in: [packages/common/src/Assert.ts:191](https://github.com/evoluhq/evolu/blob/dd96d79f1dbe9a49fa12ce8e0aa7d3d0177795ca/packages/common/src/Assert.ts#L191)

Asserts that a value is exactly `true`.

Boolean conditions preserve their control-flow narrowing, including named
type guards. Unknown values narrow to the literal `true`. Unlike
[assert](https://evolu.dev/docs/api-reference/common/Assert/variables/assert), this checks an exact boolean value instead of truthiness and
does not require a custom message.

### Example

```ts

interface User {
  readonly name: string;
}

const isUser = (value: unknown): value is User =>
  typeof value === "object" &&
  value !== null &&
  "name" in value &&
  typeof value.name === "string";

const value: unknown = { name: "Ada" };
assertTrue(isUser(value));
assertType<typeof value, User>();

const condition: unknown = true;
assertTrue(condition);
assertType<typeof condition, true>();
```

## Call Signature

```ts
function assertTrue(value: unknown): asserts value is true;
```

Defined in: [packages/common/src/Assert.ts:192](https://github.com/evoluhq/evolu/blob/dd96d79f1dbe9a49fa12ce8e0aa7d3d0177795ca/packages/common/src/Assert.ts#L192)

Asserts that a value is exactly `true`.

Boolean conditions preserve their control-flow narrowing, including named
type guards. Unknown values narrow to the literal `true`. Unlike
[assert](https://evolu.dev/docs/api-reference/common/Assert/variables/assert), this checks an exact boolean value instead of truthiness and
does not require a custom message.

### Example

```ts

interface User {
  readonly name: string;
}

const isUser = (value: unknown): value is User =>
  typeof value === "object" &&
  value !== null &&
  "name" in value &&
  typeof value.name === "string";

const value: unknown = { name: "Ada" };
assertTrue(isUser(value));
assertType<typeof value, User>();

const condition: unknown = true;
assertTrue(condition);
assertType<typeof condition, true>();
```