# assert

## Function

`assert` is used to assert that a condition is true. When the condition is true, execution continues and returns `true`; when the condition is false, a runtime error is thrown and the current execution is interrupted.

## Syntax

```bt
assert(condition)
assert(condition, message)
```

## Parameters

| Parameters | Type | Required | Default value | Description |
| ------ | ------ | ------ | ------ | ------ |
| condition | Any | Yes | None | The condition to be judged is processed according to BT's `if` truth rule. |
| message | Any | No | None | Customized failure prompt, which will be converted to string output. |

## Return value

| Type | Description |
| ------ | ------ |
| Bool | Returns `true` when the condition is true; it will not return when the condition is not true, and a runtime error will be thrown directly. |

## Code Example

```bt
assert(1 + 1 == 2)

name = 'BT'
assert(name == 'BT', 'name should be BT')

// Output: ok
print 'ok'
```

On failure:

```bt
assert(1 + 1 == 3)
```

will throw an error similar to:

```text
断言失败：assert(1 + 1 == 3)
```

## Notes

- `assert` requires at least 1 argument.
- The truth rules are consistent with the `if` condition, `null`, `empty`, `0`, empty strings, empty arrays, and empty objects are all considered false.
- When the assertion fails, the current `assert(...)` source code statement will be included in the error message as much as possible; if `message` is passed in, the custom message will be used as the main error message.