[Cycle.js] Introducing run() and driver functions

Posted 2020-06-13

Currently the code looks like :

// Logic (functional)
function main() {
  return {
    DOM: Rx.Observable.timer(0, 1000)
      .map(i => `Seconds elapsed ${i}`),
    Log: Rx.Observable.timer(0, 2000).map(i => 2*i),
  };
}

// Effects (imperative)
function DOMEffect(text$) {
  text$.subscribe(text => {
    const container = document.querySelector(‘#app‘);
    container.textContent = text;
  });
}

function consoleLogEffect(msg$) {
  msg$.subscribe(msg => console.log(msg));
}

const sinks = main();
DOMEffect(sinks.DOM);
consoleLogEffect(sinks.Log);
  

 

We still have this part of code which didn‘t wrap into a function, we can wrap into a run() function, this can provide a main enterence for the code:

function run(mainFn){
  const sinks = mainFn();
  DOMEffect(sinks.DOM);
  consoleLogEffect(sinks.Log);
}

run(main);

 

Let‘s say we want to remove consoleLogEffect, current way we need to comment out from the main() function. 

The problems are that in the first place we are hard coding these effects inside run. Instead, we should be able to specify that these are the effects that I want to run my main function, so we need to give our effects to run as well.

That will be an object. Effects functions will be an object, and the keys will match those keys that we saw from the sync here. The DOM function is DOM Effect, and the log function is consoleLogEffect.

const effects = {
    DOM: DOMEffect,
    Log: consoleLogEffect
}

function run(mainFn, effects){
  const sinks = mainFn();
  Object.keys(effects)
    .forEach( (effectKey)=>{
    effects[effectKey](sinks[effectKey]);
  })
}

run(main, effects);

 

The last thing author introduce the ‘driver‘ as the name instead of ‘effect‘ ...

// Logic (functional)
function main() {
  return {
    DOM: Rx.Observable.timer(0, 1000)
      .map(i => `Seconds elapsed ${i}`),
    Log: Rx.Observable.timer(0, 2000).map(i => 2*i),
  };
}

// Effects (imperative)
function DOMDriver(text$) {
  text$.subscribe(text => {
    const container = document.querySelector(‘#app‘);
    container.textContent = text;
  });
}

function consoleLogDriver(msg$) {
  msg$.subscribe(msg => console.log(msg));
}

function run(mainFn, drivers) {
  const sinks = mainFn();
  Object.keys(drivers).forEach(key => {
    drivers[key](sinks[key]);
  });
}

const drivers = {
  DOM: DOMDriver,
  Log: consoleLogDriver,
}

run(main, drivers);