# Configure the Client-Side Controller for a Flow Local Action

When a component is executed as a flow local action, the flow calls the `invoke` method in the client-side controller. To run the code asynchronously in your client-side controller, such as when you're making an XML HTTP request (XHR), return a Promise. When the method finishes or the Promise is fulfilled, control is returned back to the flow.

## Asynchronous Code

When a Promise is resolved, the next element in the flow is executed. When a Promise is rejected or hits the timeout, the flow takes the local action's fault connector and sets `$Flow.FaultMessage` to the error message.

By default, the error message is “An error occurred when the elementName element tried to execute the c:myComponent component.” To customize the error message in `$Flow.FaultMessage`, return it as a new Error object in the `reject()` call.

```javascript
({
   invoke : function(component, event, helper) {
      return new Promise(function(resolve, reject) {
         // Do something asynchronously, like get data from
         // an on-premise database

         // Complete the call and return to the flow
         if (/* request was successful */) {
            // Set output values for the appropriate attributes
            resolve();
         } else {
            reject(new Error("My error message")); }
      });
   }
})
```

:::note
If you’re making callouts to an external server, add the external server to the allowlist in your org and enable or configure CORS in the external server.
:::

## Synchronous Code

When the method finishes, the next element in the flow is executed.

```javascript
({
   invoke : function(component, event, helper) { 
      // Do something synchronously, like open another browser tab
      // with a specified URL

      // Set output values for the appropriate attributes
    }
 })
```

**See Also**

- [*Component Library*: lightning:availableForFlowActions Interface](https://developer.salesforce.com/docs/component-library/bundle/lightning\:availableForFlowActions/documentation)

- [Cancel an Asynchronous Request in a Flow Local Action](/docs/platform/aura-platform/guide/components-config-for-flow-actions-abort.md)

- [Using External JavaScript Libraries](/docs/platform/aura-platform/guide/js-libs-platform.md)