Why does ref.deref() ended with no result?

Hi, I am following the session to make some test, but when I execute createFourStopwatchesDemo the safari ended with not any result, it should log more infos like 'StopWatch started'...

Environment : Mac OSX 11.4 Safari Technology Prview 14.2

The Safari console only shows like below When I execute 'createFourStopwatchesDemo()'

Here is my code.

//Example1
//class with public variable and function
class StopWatchWithOneButton {
	_startTime = 0;

	click(){
		if (!this._startTime) {
			this.start();

		}else{
			this.stop();
		}
	}

	start() {
		this._startTime = Date.now();
		console.log('StopWatch started');
	}

	stop() {
		let duration = Date.now() - this._startTime;
		this._startTime = 0;
		console.log('StopWatch stopped after %d ms', duration);
	}
}


//class with private variable and function
class PrivateStopWatchWithOneButton {
	#_startTime = 0;
	static #stopWatchCount = 0;

	click(){
		if (!this.#_startTime) {
			this.#start();

		}else{
			this.#stop();
		}
	}

	#start() {
		PrivateStopWatchWithOneButton.#stopWatchCount++;
		this.#_startTime = Date.now();
		console.log('StopWatch started');
	}

	#stop() {
		PrivateStopWatchWithOneButton.#stopWatchCount--;
		let duration = Date.now() - this.#_startTime;
		this.#_startTime = 0;
		console.log('StopWatch stopped after %d ms', duration);
	}
}

function sleep(ms) {
  return new Promise(resolve => setTimeout(resolve, ms));
}

async function demo(){
	// console.log(StopWatchWithOneButton._startTime);
	var counter = new StopWatchWithOneButton();
	counter.click();

	console.log('sleep for a while,' + counter._startTime);
	await sleep(2000);
	console.log('ake up');

	counter.click();


	//private #_startTime
	var priCounter = new PrivateStopWatchWithOneButton();
	// console.log('sleep for a while of Private:' + priCounter.#_startTime);//syntax error
	priCounter.click();
	await sleep(2000);
	priCounter.click();
}


//Example2: weak reference 
//WeakRef(obj): create weak reference to an object
//use FinalizationRegistry to delete object automaticaly

const allStopWatches  = new Map();
var nextAvailableIdentifier = 1;
function removeStopwatch(identifier){
	allStopWatches.delete(identifier);
}

const finalizationRegistry = new FinalizationRegistry(removeStopwatch);

function createStopwatch(){
	let identifier = nextAvailableIdentifier++;
	let stopwatch = new StopWatchWithOneButton();

	allStopWatches.set(identifier, new WeakRef(stopwatch));
	finalizationRegistry.register(stopwatch, identifier);//the first parameter is an object

	return stopwatch;
}

function clickAllStopwatches(){
	for(let weakStopwatch in allStopWatches){
		//weakStopwatch.deref(): Get the element from the weak reference, if it still exists

		weakStopwatch.deref()?.click();
	}
}

function createFourStopwatchesDemo(){
	for (let i = 0; i < 4; i++) {
		let currStop = createStopwatch();
	}

	clickAllStopwatches();
}

Appreciate for reply in advance ~