Preserve last URL hash in /app to make going back easier

web/src/app/js/app.js

@@ -418,12 +418,18 @@ window.onload = function(e) {
 	window.onhashchange();
 }
 
+var prevHash = null;
 window.onhashchange = function(e) {
-	var path = window.location.hash.substring(1).trim();
+	try {
+		window.prevHash = new URL(e.oldURL)
+			.hash.substr(1).trim();
+	} catch (e) { window.prevHash = null }
+	var path = window.location.hash.substr(1).trim();
 	var args = path.split('/');
 	if (args.length > 0 && args[0].trim() === '')
 		args = [];
 
+	window.lastHash = path;
 	for (var i = 0; i < app.hashHandlers.length; i++) {
 		const cfg = app.hashHandlers[i];
 		if (cfg.exact !== undefined &&

web/src/app/js/base.js

@@ -142,6 +142,13 @@ function loadScript(id, file, cback) {
 	document.body.appendChild(script);
 }
 
+function hashredir(tohash, fallback) {
+	fallback = fallback || '';
+	if (tohash === undefined || tohash === null)
+		tohash = fallback;
+	window.location.href = `#${tohash}`;
+}
+
 function printstack() { console.error(new Error().stack) }
 function uuidv4() {
 	return 'xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx'.replace(/[xy]/g, function(c) {

web/src/app/js/pages/home.js

@@ -18,10 +18,10 @@ app.pages.home = {
 		setTimeout(function() {
 			document.getElementById('app-container').innerHTML = '';
 			if (app.template.isLoaded('quiz.index'))
-				window.location.href = `#quiz/${id}`
+				hashredir(`quiz/${id}`);
 		}, 80);
 		if (!app.template.isLoaded('quiz.index'))
-			window.location.href = `#quiz/${id}`;
+			hashredir(`quiz/${id}`);
 	},
 	paint: function(section, json) {
 		json = json || app.pages.home.data[section];

web/src/app/js/pages/meet.js

@@ -204,7 +204,7 @@ app.pages.meet = {
 		},
 	},
 	exit: function() {
-		window.location.href = '#';
+		hashredir(window.prevHash);
 		app.overlay.hideAll();
 	},
 	carousel: {