# Computed Properties

{% hint style="warning" %}
If you are on CBWIRE version 2.3.x  and have enabled the configuration property **useComputedPropertiesProxy**, then you will need to follow [this guide here](/v2-1/essentials/computed-properties/computed-properties-proxied.md) instead as this fundamentally changes how computed properties are referenced and accessed. 
{% endhint %}

Computed Properties are dynamic properties and are helpful for deriving values from a database or another persistent store like a cache. 

Computed Properties are similar to [Data Properties](/v2-1/essentials/properties.md) with some key differences:

* They are declared as inline functions using `computed`.
* They can return any type of CFML value or object, not just values that can be serialized and parsed by JavaScript like Data Properties.

{% hint style="success" %}
See the [Wire Lifecycle](/v2-1/essentials/lifecycle-events.md#order-of-operations) page for details on when Computed Properties are executed.
{% endhint %}

{% hint style="info" %}
Computed Properties are cached for the lifetime of the request. Meaning, if you reference your Computed Property three times in your [Template](#templates) or from within a wire [Action](/v2-1/essentials/actions.md), it will only execute once.
{% endhint %}

## Defining Properties

You can define Computed Properties on your [Wires](/v2-1/essentials/creating-components.md) using `computed`. Each Computed Property is invoked only once during a single request cycle.

```javascript
component extends="cbwire.models.Component" {

    property name="taskService" inject="taskService@myapp";

    // Computed Properties
    computed = {
        "allTasks": function() {
            return taskService.getAll();
        }
    };
}

```

## Accessing Properties

You can access your Computed Properties from within your [Actions](/v2-1/essentials/actions.md) using `computed.[propertyName]`.

```javascript
component extends="cbwire.models.Component" {

    property name="taskService" inject="taskService@myapp";

    // Computed Properties
    computed = {
        "allTasks": function() {
            return taskService.getAll();
        }
    };

    // Action
    function deleteTasks() {
        
        // Notice below we don't invoke the method using computed.allTasks().
        // We instead just use 'computed.allTasks'.
        // At this point, cbwire has rendered our computed properties
        // and overwritten the references with their result.
        if ( arrayLen( computed.allTasks ) {
            taskService.deleteAll();
        }

    }
}
```

### Getters

Getters are automatically created based on the property's name. 

In the example below, you to access the property using `this.getAllTasks()`. You can use this as an alternative to using `computed`.

```javascript
component extends="cbwire.models.Component" {

    property name="taskService" inject="taskService@myapp";

    // Computed Properties
    computed = {
        "allTasks": function() {
            return taskService.getAll();
        }
    };

    // Action
    function deleteTasks() {
        if ( arrayLen( this.getAllTasks() ) {
            taskService.deleteAll();
        }
    }
}
```

### Templates

You can access Computed Properties in your [Template](#templates) via the `args` scope.

```html
<cfoutput>
<div>
    <ul>
        <cfloop array="#args.allTasks#" index="task">
            <li>#task#</li>    
        </cfloop>
    </ul>
</div>
</cfoutput>
```


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://cbwire.ortusbooks.com/v2-1/essentials/computed-properties.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.