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Satchel is a dataflow framework based on theFlux architecture. It is characterized by exposing an observable state that makes view updates painless and efficient.

Satchel is an attempt to synthesize the best of several dataflow patterns typically used to drive a React-based UI. In particular:

• Flux is not a library itself, but is a dataflow pattern conceived for use with React. In Flux, dataflow is unidirectional, and the only way to modify state is by dispatching actions through a central dispatcher.
• Redux is an implementation of Flux that consolidates stores into a single state tree and attempts to simplify state changes by making all mutations via pure functions called reducers. Ultimately, however, we found reducers and immutable state cumbersome to deal with, particularly in a large, interconnected app.
• MobX provides a seamless way to make state observable, and allows React to listen to state changes and rerender in a very performant way. Satchel uses MobX under the covers to allow React components to observe the data they depend on.

There are a number of advantages to using Satchel to maintain your application state:

• Satchel enables a veryperformant UI, only rerendering the minimal amount necessary. MobX makes UI updates very efficient by automatically detecting specifically what components need to rerender for a given state change.
• Satchel's datastore allows forisomorphic JavaScript by making it feasible to render on the server and then serialize and pass the application state down to the client.
• Satchel supportsmiddleware that can act on each action that is dispatched. (For example, for tracing or performance instrumentation.)
• Satchel istype-safe out of the box, without any extra effort on the consumer's part.

Install via NPM:

npm install satcheljs --save

In order to use Satchel with React, you'll also need MobX and the MobX React bindings:

npm install mobx --save

npm install mobx-react --save

The following examples assume you're developing in Typescript.

import{createStore}from'satcheljs';letgetStore=createStore('todoStore',{todos:[]});

Notice the@observer decorator on the component—this is what tells MobX to rerender the component whenever the data it relies on changes.

import{observer}from'mobx-react';@observerclassTodoListComponentextendsReact.Component<any,any>{render(){return(<div>{getStore().todos.map(todo=><div>{todo.text}</div>)}</div>);}}

Note that, as a convenience, Satchel action creators created with theaction API bothcreate anddispatch the action.This is typically how you want to use action creators.If you want to create and dispatch the actions separately you can use theactionCreator anddispatch APIs.

import{action}from'satcheljs';letaddTodo=action('ADD_TODO',(text:string)=>({text:text}));// This creates and dispatches an ADD_TODO actionaddTodo('Take out trash');

You specify what action a mutator subscribes to by providing the corresponding action creator.If you're using TypeScript, the type ofactionMessage is automatically inferred.

import{mutator}from'satcheljs';mutator(addTodo,(actionMessage)=>{getStore().todos.push({id:Math.random(),text:actionMessage.text});};

Orchestrators are like mutators—they subscribe to actions—but they serve a different purpose.While mutators modify the store, orchestrators are responsible for side effects.Side effects might include making a server call or even dispatching further actions.

The following example shows how an orchestrator can persist a value to a server before updating the store.

import{action,orchestrator}from'satcheljs';letrequestAddTodo=action('REQUEST_ADD_TODO',(text:string)=>({text:text}));orchestrator(requestAddTodo,async(actionMessage)=>{awaitaddTodoOnServer(actionMessage.text);addTodo(actionMessage.text);});

In many cases a given action only needs to be handled by one mutator.Satchel provides this utility API which encapsulates action creation, dispatch, and handling in one simple function call.

TheaddTodo mutator above could be implemented as follows:

letaddTodo=mutatorAction('ADD_TODO',functionaddTodo(text:string){getStore().todos.push({id:Math.random(),text:actionMessage.text});});

This is a succinct and easy way to write mutators, but it comes with a restriction:the action creator is not exposed, so noother mutators or orchestrators can subscribe to it.If an action needs multiple handlers then it must use the full pattern with action creators and handlers implemented separately.