Middleware
Middleware lets you extend Amplitude by running a sequence of custom code on every event. This pattern is flexible and you can use it to support event enrichment, transformation, filtering, routing to third-party destinations, and more.
Note
Middleware is only supported in Maintenance Amplitude SDK except the maintenance Browser SDK and legacy Ampli. Middleware has been replaced by Plugins in the latest SDK and Ampli versions.
Middleware Structure¶
Function Signature¶
Each middleware is a simple function with this signature:
/**
* A function to run on the Event stream (each logEvent call)
*
* @param payload The `payload` contains the `event` to send and an optional `extra` that lets you pass custom data to your own middleware implementations.
* @param next Function to run the next middleware in the chain, not calling next will end the middleware chain
*/
function (payload: MiddlewarePayload: next: MiddlewareNext): void;
Types in Middleware
Name |
Type | Description |
|---|---|---|
MiddlewarePayload.event |
Event | The event data being sent. The event may vary by platform. |
MiddlewarePayload.extra |
{ [x: string]: any } | Unstructured object to let users pass extra data to middleware. |
MiddlewareNext |
(payload: MiddlewarePayload) => void | Function called at the end of each Middleware to run the next middleware in the chain. |
To invoke the next middleware in the queue, use the next function. You must call next(payload) to continue the middleware chain. If a middleware doesn't call next, then the event processing stops executing after the current middleware completes.
Payload Customization¶
Middleware access to event fields may vary by platform. To ensure comprehensive access, we recommend updating to the latest Ampli version and utilizing the Plugins feature.
For browser ampli, the following are the accessible keys under payload.
Name |
Type | Description |
|---|---|---|
event.event_type |
string | The event name. |
event.event_properties |
{ [key: string]: any } | The event properties. |
event.user_id |
string | The event level user ID. |
event.device_id |
string | The event level device ID. |
event.user_properties |
{ [key: string]: any } | The event level user properties. |
extra |
{ [x: string]: any } | The extra information you want to send that lets you pass custom data to your own middleware implementations. |
For other platforms, middleware can access and modify the entire Event JSON object, allowing for comprehensive adjustments as needed. Learn more at here.
Usage¶
Add middleware to Amplitude via amplitude.addEventMiddleware(). You can add as many middleware as you like. Each middleware runs in the order in which it's added.
amplitude.addEventMiddleware(yourMiddleware());
Middleware examples¶
Use an Middleware to modify event properties, transformation, filtering, routing to third-party destinations, and more:
Modify event properties, transformation, filtering examples
Filtering middleware example (click to expand)
amplitude.addEventMiddleware((payload, next) => {
const {eventType} = payload.event;
if (shouldSendEvent(eventType)) {
next(payload)
} else {
// event will not continue to following middleware or be sent to Amplitude
console.log(`Filtered event: ${eventType}`);
}
});
Remove PII (Personally Identifiable Information) (click to expand)
amplitude.addEventMiddleware((payload, next) => {
const { event } = payload;
if (hasPii(event.event_properties)) {
payload.event.event_properties = obfuscate(payload.event.event_properties);
}
next(payload);
});
Enrich Event Properties (click to expand)
amplitude.addEventMiddleware((payload, next) => {
const { event } = payload;
if (needsDeviceId(event)) {
payload.event.deviceId = getDeviceId();
}
next(payload)
});
Send event level groups using Ampli v1 (click to expand)
This is an example of how to send event level groups in Ampli V1. How to send event level groups in SDKs(not in Ampli) is different. Please check the specific SDKs for the usage.
ampli.addEventMiddleware((payload, next) => {
const {event, extra} = payload;
if (event && extra && event.extra.groups) {
event.groups = event.extra.groups;
}
next(payload);
});
// Pass the event level groups info though middleware extra when calling the tracking plan.
const extra = {groups: {"test_group_name": "test_group_value"}};
ampli.eventWithGroups({requiredNumber: 1.23, requiredBoolean: false}, extra);
Routing to third-party destinations example
Forward data to other services, but not Amplitude (click to expand)
import amplitude from 'amplitude/sdk'
import adroll from 'adroll';
import segment from 'segment';
import snowplow from 'snowplow';
amplitude.addEventMiddleware((payload, next) => {
const { event, extra } = payload;
segment.track(event.event_type, event.event_properties, { extra.anonymousId })
adroll.track();
snowplow.track(event.event_type, event.event_properties, extra.snowplow.context);
// next();
});
client side validation example
Use client-side validation (click to expand)
amplitude.addEventMiddleware((payload, next) => {
if (isDevelopment && !SchemaValidator.isValid(payload.event)) {
throw Error(`Invalid event ${event.event_type}`);
}
next(payload);
});