promise-timeout.js

// Promis-ifying `setTimeout`, handy to have
function timeout(ms) {
	return new Promise(resolve => setTimeout(resolve, ms));
}

// Example promise-creator. This one happens to load scripts synchronously in a browser,
// but you can work with any kind of promise here, even in node.
function getScript(src) {
	return new Promise((resolve, reject) => {
		const element = document.createElement('script');
		element.src = src;
		// May not play well with old browsers, but that's not the point of this gist
		element.onload = resolve;
		element.onerror = reject;
		// Adding to document causes network request
		document.body.appendChild(element);
	});
}

Promise.race([
	// Start loading script
	getScript('/async-script.js'),
	// If script doesn't load in 10 seconds, throw the race (timeout)
	timeout(10 * 1000).then(() => {
		throw new Error("Script did not load within 10 seconds.")
	}),
	// NOTE: timeout does not cancel the underlying network request. (script loading cannot be cancelled, anyway)
])
	// Handling for when script loads (maybe `await` this `Promise.race` expression)
	.then(console.log)
	// Handling for when script fails or times out
	.catch(console.error);