> ## Documentation Index
> Fetch the complete documentation index at: https://docs.apinizer.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Array Processing with JEXL Script

> Process arrays with for loops, aggregations, and conditional filtering using multi-line JEXL Script support in the Message Builder policy.

## Overview

The Message Builder policy supports both single-line JEXL expressions and multi-line JEXL scripts. Script mode is activated when the template expression contains `var`, `for`, `while`, or `if/else` constructs.

### Key Differences

| Feature                | JEXL Expression | JEXL Script |
| ---------------------- | --------------- | ----------- |
| Single-line evaluation | ✅               | ✅           |
| Multi-line code        | ❌               | ✅           |
| `for` loop             | ❌               | ✅           |
| `var` declaration      | ❌               | ✅           |
| `if/else` block        | ❌               | ✅           |
| `return` statement     | ❌               | ✅           |

***

## Example 1: Converting a Tag Array to a JSON Array

### Input Body

```json theme={null}
{
  "tags": [
    { "id": 1, "name": "outdoor" },
    { "id": 2, "name": "premium" },
    { "id": 3, "name": "sale" }
  ]
}
```

### Template (JEXL Script)

```
#{
  var result = '[';
  var first = true;
  for (tag : body.$.tags) {
    if (!first) { result = result + ','; }
    result = result + '"' + tag.name + '"';
    first = false;
  }
  result + ']'
}
```

<Note>
  Body variables extracted via JSONPath are automatically converted to Java `List` or `Map` objects, so they support `.size()` and index access.
</Note>

### Expected Output

```json theme={null}
["outdoor","premium","sale"]
```

***

## Example 2: Summing Order Items

### Input Body

```json theme={null}
{
  "items": [
    { "name": "Book", "price": 29.99, "quantity": 2 },
    { "name": "Pen", "price": 4.50, "quantity": 5 },
    { "name": "Notebook", "price": 12.00, "quantity": 3 }
  ]
}
```

### Template (JEXL Script)

```
#{
  var total = 0;
  for (item : body.$.items) {
    total = total + (item.price * item.quantity);
  }
  total
}
```

### Expected Output

```
118.48
```

***

## Example 3: Conditional Array Filtering

Filter array elements that meet a specific condition and build a new array.

### Input Body

```json theme={null}
{
  "products": [
    { "name": "Laptop", "stock": 0 },
    { "name": "Phone", "stock": 15 },
    { "name": "Tablet", "stock": 0 },
    { "name": "Monitor", "stock": 8 }
  ]
}
```

### Template (JEXL Script)

```
#{
  var result = '[';
  var first = true;
  for (p : body.$.products) {
    if (p.stock > 0) {
      if (!first) { result = result + ','; }
      result = result + '"' + p.name + '"';
      first = false;
    }
  }
  result + ']'
}
```

### Expected Output

```json theme={null}
["Phone","Monitor"]
```

***

## Example 4: Role-Based Authorization with if/else

Assign an authorization level based on user roles.

### Setup

Assume a custom variable `userRoles` is already populated (e.g., from the request body) with value `["admin","editor"]`.

### Template (JEXL Script)

```
#{
  var roles = userRoles;
  var level = 'NONE';
  for (var role : roles) {
    if (role == 'admin') {
      level = 'FULL';
    } else if (role == 'editor' && level != 'FULL') {
      level = 'WRITE';
    } else if (role == 'viewer' && level == 'NONE') {
      level = 'READ';
    }
  }
  level
}
```

### Result

| Roles                 | `authLevel` Value |
| --------------------- | ----------------- |
| `["admin"]`           | `FULL`            |
| `["editor","viewer"]` | `WRITE`           |
| `["viewer"]`          | `READ`            |
| `[]`                  | `NONE`            |

***

## Example 5: Accessing Array Elements with `$[n]` Syntax

To access a specific element of a root-level array, use `$[n]` syntax.

### Input Body (Root Array)

```json theme={null}
[
  { "id": 1, "name": "First" },
  { "id": 2, "name": "Second" }
]
```

### Variable Reference in Template

```
#{body.$[0].name}
```

### Output

```
First
```

<Tip>
  `$[0]` refers to the first element of the root array. `$[1].id` would return the `id` of the second element.
</Tip>

***

## Tips and Common Mistakes

<AccordionGroup>
  <Accordion title="How do I reference body array variables?">
    Use the standard `body.$.path` syntax directly inside the JEXL script. For example, `for (tag : body.$.tags)` iterates over the tags array. JSON array and object values are automatically converted to Java `List` and `Map` objects, enabling iteration and property access.
  </Accordion>

  <Accordion title="Can I use the `return` keyword?">
    Yes, in JEXL Script mode you can use `return value` explicitly. However, returning a value from the last expression (as in examples above) is the recommended approach.
  </Accordion>

  <Accordion title="Can I include `{` and `}` inside script templates?">
    Yes. The Message Builder uses a balanced brace scanner to correctly identify `#{}` blocks, including those with nested curly braces such as JSON object literals.
  </Accordion>

  <Accordion title="Can I use while loops?">
    Yes, JEXL Script supports `while` loops as well:

    ```
    #{
      var list = body.$.items;
      var i = 0;
      var sum = 0;
      while (i < list.size()) {
        sum = sum + list[i].value;
        i = i + 1;
      }
      sum
    }
    ```
  </Accordion>
</AccordionGroup>