Wait for a key in JS

wait-for-key.js

/** Wait for the given key; if key is omitted, any key will trigger. It resolves the event. */
function waitForKey(key){
	return new Promise(resolve => {
		var onkeydown = e => {
			if(typeof key === 'undefined' || e.key === key){
				document.removeEventListener('keydown', onkeydown);
				resolve(e);
			}
		};
		document.addEventListener('keydown', onkeydown);
	});
};