Use Yield within the Scheduler API to break up long JavaScript tasks [🟥 awaiting full support]

[chrisblakley]

https://developer.chrome.com/blog/introducing-scheduler-yield-origin-trial

As of Chrome 129, functions can yield back to the main thread by using await scheduler.yield();

Google recommends using it liberally throughout the codebase, but I want to start with just the biggest functionality first.

Edit: Now on CanIUse: https://caniuse.com/mdn-api_scheduler_yield

[chrisblakley]

Quick notes, the function that this is within must be an async function and if scheduler.yield is not a function the JavaScript will error. So this cannot be implemented until full browser support– because I don't want to add a bunch of these throughout Nebula and then have to remove them all later...

if ( "scheduler" in window && "yield" in scheduler ){
	await scheduler.yield();
}

[chrisblakley]

Great article on this: https://www.debugbear.com/blog/scheduler-yield

[chrisblakley]

Added comments throughout Nebula for where I intend to place these when available.

//@todo "Nebula" 0: Scheduler Yield here when fully supported

These are placed in functions that are already async as well as functions that are not. Would need to test if changing non-async functions into async (and enabling the yield) breaks any functionality.

[chrisblakley]

Could use this function in the meantime...

//A function for shimming scheduler.yield with no fallback:
function yieldToMain () {
	//Use scheduler.yield if it exists
	if ( 'scheduler' in window && 'yield' in scheduler ){
		return scheduler.yield();
	}
	
	return; //Fall back to nothing (no yielding)
}

// Example usage:
async function doWork(){
	// Do some work:
	// ...
	
	await yieldToMain();
	
	// Do some other work:
	// ...
}

[chrisblakley]

Ok I have grown on the idea of using a shim function in the meantime while we wait for browser support.

//Yield back to the main thread when supported by the browser. Otherwise, do nothing.
nebula.yield = function(){
	//Use scheduler.yield if it exists
	if ( 'scheduler' in window && 'yield' in scheduler ){
		return scheduler.yield();
	}

	return; //Fall back to nothing (no yielding)
};

Use it like this:

await nebula.yield();

This is now used in several places throughout Nebula and can also be used in the child theme.

Just remember that the function needs to be async which means that it returns a promise! Anything calling an async function must expect a promise (and not a specific value) returned. So they can either use .then() on the function or await it. Otherwise, avoid trying to yield in that function.

[chrisblakley]

I also wrote a nebula.each() function that can be awaited to avoid race conditions while preserving the flexibility and convenience of jQuery.each().

https://nebula.gearside.com/functions/each/

[chrisblakley]

https://caniuse.com/mdn-api_scheduler_yield