Meiosis Tutorial

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08 - Using React

In the 06 - Components lesson, we created the state management code for an example with a conditions component and two temperature components, air and water.

In this section, we'll wire this up to React.

Wiring Meiosis

Remember that we had an actions object and a states stream:

var actions = app.Actions(update);
states.map(function(state) {
  document.write("<pre>" + JSON.stringify(state, null, 2) + "</pre>");
});

Now, we'll use ReactDOM.render and a React component to render the view. We'll pass the actions and states props to a top-level App component:

ReactDOM.render(<App states={states} actions={actions} />,
  document.getElementById("app"));

Within the App component, we'll use map on the states stream and call setState so that the view gets refreshed whenever the state changes.

The App Component

The App component retrieves states and actions from the passed-in props. We initialize a React hook with useState from the first value of the states stream. Then, we map the states stream and call setState to set the hook state.

var App = function({ states, actions }) {
  var [init, setInit] = React.useState(false);
  var [state, setState] = React.useState(states());

  if (!init) {
    setInit(true);
    states.map(setState);
  }

  return (<div>
    <Conditions state={state} id="conditions" actions={actions} />
    <Temperature state={state} id="temperature:air" actions={actions} />
    <Temperature state={state} id="temperature:water" actions={actions} />
    <pre>{JSON.stringify(state, null, 4)}</pre>
  </div>);
}

The Conditions Component

The Conditions component displays a checkbox for "precipitations" and a series of radio butons for the sky (Sunny, Cloudy, Mix of sun/clouds). The state is used to reflect the current state, and actions are called to update the state when the user changes the checkbox and radio buttons:

var SkyOption = function({ state, id, actions, value, label }) {
  return (<label>
    <input type="radio" id={value} name="sky"
      value={value} checked={state[id].sky === value}
      onChange={evt => actions.changeSky(id, evt.target.value)}/>
    {label}
  </label>);
};

var Conditions = function({ state, id, actions }) {
  return (
    <div>
      <label>
        <input
          type="checkbox"
          checked={state[id].precipitations}
          onChange={evt =>
            actions.togglePrecipitations(id, evt.target.checked)
          }/>
        Precipitations
      </label>
      <div>
        <SkyOption state={state} id={id} actions={actions} value="SUNNY"
          label="Sunny"/>
        <SkyOption state={state} id={id} actions={actions} value="CLOUDY"
          label="Cloudy"/>
        <SkyOption state={state} id={id} actions={actions} value="MIX"
          label="Mix of sun/clouds"/>
      </div>
    </div>
  );
};

The Temperature Component

The Temperature component is similar:

var Temperature = function({ state, id, actions }) {
  return (<div>
    {state[id].label} Temperature:
    {state[id].value} &deg; {state[id].units}
    <div>
      <button
        onClick={() => actions.increment(id, 1)}>
        Increment
      </button>
      <button
        onClick={() => actions.increment(id,-1)}>
        Decrement
      </button>
    </div>
    <div>
      <button
        onClick={() => actions.changeUnits(id)}>
        Change Units
      </button>
    </div>
  </div>);
};

You can see the complete example below.

Takeaways

We can wire up Meiosis to React with a hook. We map the states stream to call setState to update the state and automatically refresh the view.

Then, all other React components in the application are consistent: they all receive state and actions props. When rendering other components, state and actions are passed along. When a component is used multiple times, or when you want to define the state property outside of the component, you also pass the id.

Components can then use the state to render the view according to the current application state, and call actions to trigger changes.

Conclusion

This concludes the Meiosis tutorial. See 11 - What's Next? for ideas on where to go from here.

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Meiosis is developed by @foxdonut00 / foxdonut and is released under the MIT license.