Built-in middleware

elfi provides some builtin middleware. You’ll find documentation about them in this document.

logger (source)

This middleware is used to log each change to whatever logging system you are using (a simple console.log by default)

import { createStore } from "elfi"
import createLoggerMiddleware from "elfi/middleware/logger"

const logger = createLoggerMiddleware()

const store = createStore(1, [logger])

You can define a custom logger by passing a function to createLoggerMiddleware. This function accepts a single argument which is object with the following shape {oldState, newState, change, args}.

import { createStore } from "elfi"
import createLoggerMiddleware from "elfi/middleware/logger"

function logOldState({ oldState }) {
  console.log(oldState)
}

const logger = createLoggerMiddleware(({ oldState }) => console.log(oldState))

const store = createStore(1, [logger])

versioning (source)

This middleware is used to add a version number to the state without triggering another state change.

import { createStore } from "elfi"
import createVersioningMiddleware from "elfi/middleware/versioning"

const versioning = createVersioningMiddleware()

const store = createStore(1, [versioning])

By default, it acts as if state is a simple object and sets the version field of that object. You will probably want to define how to set the version and for this you can pass a custom setter function to createVersioningMiddleware.

It will be called with the new state as the sole argument. Here’s an example with Immutable.js:

import Immutable from "immutable"
import { createStore } from "elfi"
import createVersioningMiddleware from "elfi/middleware/versioning"

const versioning = createVersioningMiddleware(state =>
  state.set((state.get("version") || 0) + 1),
)
const store = createStore(new Immutable.Map(), [versioning])