[[_policy_js]]
=== JavaScript-Based Policy

You can use this type of policy 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 <<fake/../evaluation-api.adoc#_policy_evaluation_api, Evaluation API>>.

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

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

==== Configuration

* *Name*
+
A human-readable and unique string describing the policy. A best practice is to use names that are closely related to your business and security requirements, so you
can identify them more easily.
+
* *Description*
+
A string containing details about this policy.
+
* *Code*
+
The JavaScript code providing the conditions for this policy.
+
* *Logic*
+
The <<fake/../logic.adoc#_policy_logic, 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 role-based access control (RBAC):

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

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

Or a combination of several 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 an object implementing *org.keycloak.authorization.policy.evaluation.Evaluation*. For more information about what you can access from this interface, see the <<fake/../evaluation-api.adoc#_policy_evaluation_api, Evaluation API>>.