added a cancel option to popups (closes #28)

src/js/main.js

@@ -108,15 +108,17 @@
 
 	// start a new game
 	startGame=async (category, levelId, filename) => {
-		// stop any running games
+		// stop any running games and clear popups
 		stopGame();
+		Popup.dismiss();
 
 		// load rules and level from cache or server
 		const rules=levelList[category].rules || {};
 		const level=await levels.get(filename);
 
-		// stop any running games again
+		// stop any running games and clear popups again
 		stopGame();
+		Popup.dismiss();
 
 		// create the game and attach the callbacks and config
 		const snek=currentGame=new SnekGame(level, canvas, rules);
@@ -153,11 +155,13 @@
 	// return to the menu
 	menu=() => {
 		stopGame();
+		Popup.dismiss();
 	};
 
 	// show config editor
 	settings=async () => {
 		stopGame();
+		Popup.dismiss();
 		await configEditor.show();
 		location.hash='menu';
 	};
@@ -165,6 +169,7 @@
 	// show help page
 	help=async () => {
 		stopGame();
+		Popup.dismiss();
 		let iframe=document.createElement('iframe');
 		iframe.src='help.html';
 		iframe.style.width='100%';

src/js/popup.js

@@ -77,15 +77,20 @@ class Popup {
 		buttons.forEach(btn => buttonSection.appendChild(btn));
 
 		parent.appendChild(outer);
+		Popup.displayed.push(this);
 
-		const code=await Promise.race(buttons.map(btn => new Promise(ok => {
+		const btnActions=buttons.map(btn => new Promise(ok => {
 			btn.addEventListener('click', e => {
 				e.preventDefault();
 				return ok(btn.dataset.code);
 			});
-		})));
+		}));
+		const dismissAction=new Promise(ok => this.dismiss=ok);
+
+		const code=await Promise.race(btnActions.concat([dismissAction]));
 
 		parent.removeChild(outer);
+		Popup.displayed.splice(Popup.displayed.indexOf(this), 1);
 		return code;
 	}
 }
@@ -93,4 +98,9 @@ class Popup {
 Popup.EM=Symbol('EM');
 Popup.STRONG=Symbol('STRONG');
 
+Popup.displayed=[];
+Popup.dismiss=arg => {
+	Popup.displayed.forEach(p => p.dismiss(arg));
+};
+
 return module.exports=Popup;