Middleware

Middleware allows you to hook into the dispatch pipeline in order to be notified of every action that is dispatched, and even modify or intercept the action.

Creating middleware

Middleware is simply a function with the following signature:

function sampleMiddleware(next, actionMessage)

next: The next step in the dispatch pipeline. It is a function that takes actionMessage as a parameter. Every middleware should call next at some point (unless it wants to prevent the action from being dispatched further).

actionMessage: The action message object.

Example

The following is a simple middleware that traces each action to the console:

import { ActionMessage, DispatchFunction } from 'satcheljs';

function traceMiddleware(next: DispatchFunction, actionMessage: ActionMessage) {
    console.log("Dispatching action: " + actionMessage.type);
    next(actionMessage);
}

Installing middleware

You tell Satchel to use your middleware by calling applyMiddleware. Calling applyMiddleware will replace any current middleware with the list of middleware you provide.

import { applyMiddleware } from 'satcheljs';

applyMiddleware(traceMiddleware, middleware2, middleware3);