Support trait for signal

[anuoua]

Like the new js signal proposal, the equals function is passed in the second parameter to determine whether the object has changed.

Scenario: Many times we encounter persistent instances, their references never change, but their properties do. The signal is never perceived.

[tomByrer]

Another Scenario: you want to throttle results (eg for a search input, typically you pause new searches until there is a pause in typing), so you use the second parameter to gate the signal getting through.

[tomByrer]

BTW @anuoua, you might want to check out this for nested object signaling:
https://github.com/CCherry07/alien-deepsignals

[johnsoncodehk]

This is intentionally unsupported, as it limits the possibility of early returns during comparison.

Here are a workaround to do it:

computed(prevValue => {
	const newValue = yourGetter();
	if (yourEqualsMethod(prevValue, newValue)) {
		return prevValue;
	}
	return newValue;
});

To keep the implementation minimal we will not implement the proposal API in alien-signals, but you can track: proposal-signals/signal-polyfill#44