== JavaScript-Based Policy

This type of policy allows you to define conditions for your permissions using JavaScript. It is one of the _Rule-Based_ policy types
supported by {{book.project.name}}, and provides flexibility to write any policy based on the link:evaluation-api.adoc[Evaluation API].

To create a new JavaScript-based policy, select the option *JavaScript* in the dropdown located in the right upper corner of the permission listing.

.Add JavaScript Policy
image:../../images/policy/create-js.png[alt="Add JavaScript Policy"]

=== Configuration

* *Name*
+
A human-readable and unique string describing the policy. We strongly suggest that you use names that are closely related with your business and security requirements, so you
can identify them more easily and also know what they actually mean.
+
* *Description*
+
A string with more details about this policy.
+
* *Code*
+
The JavaScript code providing the conditions for this policy.
+
* *Logic*
+
The link:logic.html[Logic] of this policy to apply after the other conditions have been evaluated.

=== Examples

Here is a simple example of a JavaScript-Based policy that uses Attribute-Based Access Control (ABAC) to define a condition based on an attribute
obtained from the execution context:

```javascript
var context = $evaluation.getContext();
var contextAttributes = context.getAttributes();

if (contextAttributes.containsValue('kc.client.network.ip_address', '127.0.0.1')) {
    $evaluation.grant();
}
```

You can also use RBAC:

```javascript
var identity = $evaluation.getIdentity();

if (identity.hasRole('keycloak_user')) {
    $evaluation.grant();
}
```

Or even a mix of different access control mechanisms:

```javascript
var context = $evaluation.getContext();
var identity = context.getIdentity();
var attributes = identity.getAttributes();
var email = attributes.getValue('email').asString(0);

if (identity.hasRole('admin') || email.endsWith('@keycloak.org')) {
    $evaluation.grant();
}
```

When writing your own rules, keep in mind that the *$evaluation* object is just a object implementing *org.keycloak.authorization.policy.evaluation.Evaluation*. For more details about what you can access from this interface,
see link:evaluation-api.adoc[Evaluation API].