> For the complete documentation index, see [llms.txt](https://boxlang.ortusbooks.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://boxlang.ortusbooks.com/boxlang-language/reference/components/system/param.md).

# Param

Tests for a parameter's existence, tests its data type, and, if a default value is not assigned, optionally provides one.

## Component Signature

```
<bx:Param name=[string]
type=[string]
default=[function]
max=[numeric]
min=[numeric]
pattern=[string] />
```

### Attributes

| Atrribute | Type       | Required | Description                                                                                          | Default |
| --------- | ---------- | -------- | ---------------------------------------------------------------------------------------------------- | ------- |
| `name`    | `string`   | `true`   | The name of the parameter                                                                            |         |
| `type`    | `string`   | `false`  | The data type of the parameter                                                                       |         |
| `default` | `function` | `false`  | The default value of the parameter. Compiled expressions are deferred until the variable is missing. |         |
| `max`     | `numeric`  | `false`  | The maximum value of the parameter                                                                   |         |
| `min`     | `numeric`  | `false`  | The minimum value of the parameter                                                                   |         |
| `pattern` | `string`   | `false`  | The pattern of the parameter                                                                         |         |

## Examples

### bx:param in BL

A very basic BL bx:param example

```java
<bx:param name="userID" default="0"/>
```

### bx:param in script

A very basic script bx:param example

[Run Example](https://try.boxlang.io/?code=eJxLqrAqSCxKzFXIS8xNtVUqLU4t8nRRUkhJTUsszSmxNbDmSiKoAgArtxbV)

```java
bx:param name="userID" default=0;
bx:param name="userID" default=0;

```

### Tag syntax using a regex

Throws an error if the value is not one of a list of possible values

```java
<bx:param name="sortdir" default="ASC" type="regex" pattern="ASC|DESC"/>
```


---

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