Jolly Roger

~2KB micro-framework on top of React hooks.

• Online demo 🚀
• Jolly Roger visualized 🔍

---

• Installation
• Concepts
  • Sharing state
  • Using a reducer
  • Using the context
• API
  • useState(slice, initial value)
  • useReducer(slice, actions)
  • useContext()
  • context(functions)

Installation

npm install jolly-roger or yarn add jolly-roger

or

https://unpkg.com/jolly-roger@latest/umd/jr.js

Concepts

The hooks API is a wonderful idea. There are some slick patterns involved which pushes the React development to a more functional approach. I was really interesting to try that new API and decided to use it for my latest project. It looked like I can't build my app only with hooks. I needed something else. And that's mainly because each hook works on a local component level. I can't really transfer state or exchange reducers between the components. That's why I created this library. It has similar helpers but works on a global app level.

Sharing state

Let's have a look at the following example:

import react, { useEffect, useState } from 'react';
 
const App = function () {
  const [ time, setTime ] = useState(new Date());
  
  useEffect(() => {
    setInterval(() => setTime(new Date()), 1000);
  }, [])
  
  return (
    ...
  );
}

It's a component that has a local state called time. Once we mount it we trigger an interval callback and change the state every second. Now imagine that we want to use the value of time in another component. What if we want to render it by using a Clock and a Watch components like so:

function Clock() {
  const [ time ] = useState(<?>);
  
  return <p>Clock: { time.toTimeString() }</p>;
}
 
function Watch() {
  const [ time ] = useState(<?>);
  
  return <p>Watch: { time.toTimeString() }</p>;
}

That's not really possible because the idea of the useState hook is to create a local component state. So time is available only for the App but not Clock and Watch. This is the first problem that this library solves. It gives you a mechanism to share state between components.

function Clock() {
  const [ time ] = roger.useState('time');
  
  return <p>Clock: { time.toTimeString() }</p>;
}
 
function Watch() {
  const [ time ] = roger.useState('time');
  
  return <p>Watch: { time.toTimeString() }</p>;
}
 
const App = function () {
  const [ time, setTime ] = roger.useState('time', new Date());
  
  useEffect(() => {
    setInterval(() => setTime(new Date()), 1000);
  }, [])
  
  return (
    <Fragment>
      <Clock />
      <Watch />
    </Fragment>
  );
}

Here is a online demo.

The API is almost the same except we have to give the state a name. In this case that is the first argument of the Roger's useState equal to time. We have to give it a name because we need an identifier to access it from within the other components.

Using a reducer

Now when we have a global state we may define a reducer for it. You know that nice idea of having a function that accepts your current state and an action and returns the new version of the state in a immutable fashion. Let's build on top of the previous example and say that we will set the time manually. We are going to dispatch an action giving the new time value and the reducer has to update the state.

roger.useReducer('time', {
  yohoho(currentTime, payload) {
    console.log('Last update at ' + currentTime);
    console.log('New ' + payload.now);
    return payload.now;
  }
});

Again the important bit here is the name time because that's how Roger knows which slice of the global state to manipulate. In here we are creating an action with a name yohoho that receives the current time and some payload. In this example we don't want to do anything else but simply set a new time so we just return what's in the now field. We will also create a new component that will trigger this action:

function SetNewTime() {
  const { yohoho } = roger.useContext();
  
  return (
    <button onClick={ () => yohoho({ now: new Date() }) }>
      click me
    </button>
  );
}

The rest is the same. Here is a online demo to play with.

What's this useContext read in the next section.

Using the context

Because Roger works as a global singleton it can store some stuff for you. By default the actions that we define in our useReducer calls are automatically stored there. As we saw in the previous section the yohoho method is used by getting it from the Roger's context. We can do that with the help of useContext method. Let's continue with our little time app and get the time from a external API via a fetch call. In this case we may create a function in the Roger's context that does the request for us and fires the yohoho action.

roger.context({
  async getTime(url, { yohoho }) {
   	const result = await fetch(url);
    const data = await result.json();
    
    yohoho({ now: new Date(data.now)})
  }
});

Every context method accepts two arguments. The first one is reserved for anything that may need to be injected as a dependency and the second one is always the Roger's context itself. In our case getTime has one dependency and that's the endpoint URL. We need the yohoho action defined in our useReducer call. We get the data and dispatch the action.

Here is the same <SetNewTime> component using the new getTime helper:

function SetNewTime() {
  const [ inProgress, setProgress ] = useState(false);
  const { getTime } = roger.useContext();
  
  const onClick = async () => {
    setProgress(true);
    await getTime('https://igit.dev/now');
    setProgress(false);
  }
  
  return (
    <button onClick={ onClick } disabled={ inProgress }>
      { inProgress ? 'getting the time' : 'click me' }
   	</button>
  );
}

Notice that Jolly Roger plays absolutely fine with the native React hooks. Like we did here we set a inProgress flag to indicate that there is a request in progress. Check out how it works here.

API

useState(slice, initial value)

	type	description
slice	<string>	A name of the slice in the application state
initial value	<any>	Initial value which is set in the state
returns	<array>	Returns an array where the first item is the state value and the second a function to change it

Example:

// inside your component
const [ counter, setCounter ] = roger.useState('counter', 10);
 
// later in the same component
setState(20);
...
 
return <p>{ counter }</p>; // after re-render you'll get: <p>20</p>

Online demo

useReducer(slice, actions)

	type	description
slice	<string>	A name of the slice in the application state
actions	<object>	An object which keys are the name of the actions and values are the actual reducer functions. Every reducer receives the current state value and should return the new one. As second argument the reducer accepts the action's payload (if any)
returns	nothing

Example:

// this is out of your React components
roger.useReducer('counter', {
  increment(number, payload) {
    return number + payload.amount;
  }
});
 
// in your React component
const [ counter ] = roger.useState('counter', 10);
const { increment } = roger.useContext();
 
// later in the same component
increment({ amount: 4 });
...
 
return <p>{ counter }</p>; // after re-render you'll get: <p>14</p>

Online demo

useContext()

	type	description
returns		A Jolly Roger context where you'll find all the reducer actions + all the functions defined via the context method.

Example:

// outside of your React components
roger.context({
  greeting(name) {
    return `Hello ${ name }`;
  }
});
 
// in your React component
const { greeting } = roger.useContext();
 
return <p>{ greeting('John') }</p>; // <p>Hello John</p>

Online demo

context(functions)

	type	description
functions	<object>	An object which keys are the function names and values are the actual function definitions. Every function receives a parameter as a first argument. As second argument it accepts the Roger's context. In that context object you'll find the other context functions and also the reducer actions defined while using useReducer.
returns	nothing

roger.useReducer('time', {
  setTime(currentTime, { newTime }) {
    return newTime;
  }
})
roger.context({
 	logTime(time) {
    console.log(time);
  },
  async getTime(url, { logTime, setTime }) {
   	const result = await fetch(url);
    const data = await result.json();
    
    logTime(data.now); // another context method
    setTime(data.now); // reducer action
  }
});

Online demo