Event handler functions

Understand when EdgeWorker scripts are executed.

The EdgeWorkers code is invoked based on specific HTTP events.

The responseProvider event handler acts as a surrogate origin to execute EdgeWorkers code. To learn how more, go to the Response Orchestration section.

onClientRequest: This event happens for every request as the request is received, before checking if a response is available in cache. Use this event for request modifications before going to cache or to origin. Here’s an example of a function that modifies the response based on user location:
```
// redirect based on originating country of request
 
export function onClientRequest(request) {
   var country = request.userLocation.country;
    if (country === 'FR') {
       request.respondWith(302, {'Location': ['https://www.example.com/fr/']}, '');
    }
}
```
onOriginRequest: This happens just before sending the request to the origin. This event only happens if the response is not served from cache and not constructed on the edge. Use this event if you want to affect the response coming back from the origin. This function adds a device type header to the origin request:
```
// send header to origin
 
export function onOriginRequest(request) {
   if (request.device.isMobile) { 
      request.setHeader('X-MyHeader-DeviceType','Mobile'); 
   } 
   else if (request.device.isTablet) { 
      request.setHeader('X-MyHeader-DeviceType', 'Tablet'); 
   } 
   else { 
      request.setHeader('X-MyHeader-DeviceType', 'Desktop'); 
   }
}
```
onOriginResponse: This event happens as the origin response is created. The event only happens if the response is not served from cache and not constructed on the edge. Use this event if you want to modify the response before it is cached.
```
// remove header returned from origin
 
export function onOriginResponse(request, response) {
response.removeHeader('InternalDebugHeader');
}
```
onClientResponse: This event happens before the response is sent to the client.
Note: You cannot currently modify the response body. You can only modify the response headers.
This example shows how to set a header before the response is sent to the client:
```
// add response header
 
export function onClientResponse(request, response) {
response.addHeader('Powered-By','Akamai EdgeWorkers');
}
```

responseProvider: This event happens if the response is not already found in cache. This example shows how to return a response body:

//add content to the response

export function responseProvider(request) {
return Promise.resolve(createResponse(200, {}, "<html><head></head><body><p>Hello World</p></body></html>"));
}

Note: To find more information about how EdgeWorker scripts are executed during the responseProvider event go to the Response Orchestration section.

To create a function for any of these events, implement the callbacks as explained in the JavaScript reference.