yskszk63/index.html

## index.html
<!DOCTYPE html>

<html>
  <head>
    <meta charset="utf-8" />
    <title>Async Iterator</title>
  </head>
  <body>
    <pre></pre>
    <script src="script.js"></script>
  </body>
</html>
<!-- vim:set sw=2 ts=2: -->

## script.js
async function main() {
    for await (const event of iterEvents(document, 'click')) {
        log(event, event.target);
        if (event.target.matches('pre')) {
            throw new Error("pre clicked");
        }
    }
}

function log(...s) {
    document.querySelector('pre')
        .appendChild(new Text(s.map(String).join(' ') + '\n'));
}

class Deferred {
    constructor() {
        this.promise = new Promise((resolve, reject) => {
            this.resolve = resolve;
            this.reject = reject;
        });
    }
}

async function* iterEvents(element, type) {
    let signal = null;
    const results = [];
    let done = false;

    function handler(event) {
        if (signal) {
            signal.resolve();
        }
        results.push(event);
    }

    log("begin");
    element.addEventListener(type, handler);
    try {
        while (!done) {
            if (!results.length) {
                signal = new Deferred();
                await signal.promise;
                signal = null;
            } else {
                yield results.shift();
            }
        }
    } finally {
        element.removeEventListener(type, handler);
        log("end");
    }
}

main();
	<!DOCTYPE html>

	<html>
	<head>
	<meta charset="utf-8" />
	<title>Async Iterator</title>
	</head>
	<body>
	<pre></pre>
	<script src="script.js"></script>
	</body>
	</html>
	<!-- vim:set sw=2 ts=2: -->
	async function main() {
	for await (const event of iterEvents(document, 'click')) {
	log(event, event.target);
	if (event.target.matches('pre')) {
	throw new Error("pre clicked");
	}
	}
	}

	function log(...s) {
	document.querySelector('pre')
	.appendChild(new Text(s.map(String).join(' ') + '\n'));
	}

	class Deferred {
	constructor() {
	this.promise = new Promise((resolve, reject) => {
	this.resolve = resolve;
	this.reject = reject;
	});
	}
	}

	async function* iterEvents(element, type) {
	let signal = null;
	const results = [];
	let done = false;

	function handler(event) {
	if (signal) {
	signal.resolve();
	}
	results.push(event);
	}

	log("begin");
	element.addEventListener(type, handler);
	try {
	while (!done) {
	if (!results.length) {
	signal = new Deferred();
	await signal.promise;
	signal = null;
	} else {
	yield results.shift();
	}
	}
	} finally {
	element.removeEventListener(type, handler);
	log("end");
	}
	}

	main();