[Signal] 1 - Basic version of signal

Implement two functions of Signals

• createSignal: return a tuple with read function and wrtie function
• createEffect: accept a function which will be executed when signal value changed

Code to test:

import { createSignal } from "./reactivy";

const [count, setCount] = createSignal(0);

console.log(count()); // 0
setCount(5);
console.log(count()); // 5

Version 1 - CreateSignal

export function createSignal(value) {
  const read = () => value;
  const write = (newValue) => {
    value = newValue;
  };
  return [read, write];
}

Version 2 - CreateSignal & CreateEffect

Code to test:

import { createSignal, createEffect } from "./reactivy";

const [count, setCount] = createSignal(0);

createEffect(() => {
  console.log(count());
});

setCount(5);

• stack: global state, everytime createEffectis called, will be added into stack
• subscribers: for readfunction, get effect, add to subscribers, so that when value change, can notify signals

const stack = []

export function createSignal(value) {
  const subscribers = new Set();
  const read = () => {
    // check is there any effect runnning?
    // if yes, then add to subscribers
    const observer = stack[stack.length - 1];
    if (observer) {
      subscribers.add(observer);
    }
    return value;
  };
  const write = (newValue) => {
    value = newValue;
    // notify all the subscribers there is changes
    for (const observer of subscribers) {
      // add effect to the stack again
      observer.execute();
    }
  };
  return [read, write];
}

export function createEffect(fn) {
    const effect = {
       execute() {
           stack.push(effect);
           fn();
           stack.pop();
       }
    };
    
    effect.execute();
}