Difference between effect and useSignalEffect in signals-react

Question

This question is not an issue, it is for educational purpose.

I was trying out effect and useSignalEffect from @preact/signals-react in react application. Problem is i see effect and useSignalEffect have same behaviour they both run when the subscribed signal changes. Could anybody clearify on whats the difference between them.

Example I have used:

import React from 'react'
import {effect,  useSignal,useSignalEffect } from '@preact/signals-react'


export default function ComputedSignalExample() {
    const count = useSignal(0);

    useSignalEffect(() => {
      console.log(`From useSignalEffect: ${count}`); 
    });

    effect(() => {
        console.log(`From Effect: ${count}`); 
    });
  
    return (
      <div>
        <p>The current count is: {count}</p>
        <button onClick={() => count.value++}>Increment</button>
      </div>
    );
  }

From Effect: 0
From useSignalEffect: 0
From Effect: 1
From useSignalEffect: 1
From Effect: 2
From useSignalEffect: 2

I used useSignalEffect with a dependency array, to see if it might have same setup as useEffect react hook, but seems like, it doesn't care about dependency array.

useSignalEffect(() => {
  console.log('From useSignalEffect');
},[count]);

Also tried this, but no effect:

useSignalEffect(() => {
  console.log('From useSignalEffect');
},[count.value]);

Answer 1

The docs explicitly state what this is for:

If you need to instantiate new signals or create new side effects on signal changes inside your components, you can use the useSignal, useComputed and useSignalEffect hooks.

https://github.com/preactjs/signals/tree/main/packages/react#hooks

Don't use effect in components, it will be recreated (and resubscribe) upon every single rerender of your component. For a console.log(), this won't have much of an impact, but heavier effects could.