Introduce background actions and media query tracker mechanisms

core/modules/filter-tracker.js

@@ -0,0 +1,87 @@
+/*\
+title: $:/core/modules/filter-tracker.js
+type: application/javascript
+module-type: global
+
+Class to track the results of a filter string
+
+\*/
+(function(){
+
+/*jslint node: true, browser: true */
+/*global $tw: false */
+"use strict";
+
+function FilterTracker(wiki) {
+	this.wiki = wiki;
+	this.trackers = [];
+	this.wiki.addEventListener("change",this.handleChangeEvent.bind(this));
+}
+
+FilterTracker.prototype.handleChangeEvent = function(changes) {
+	this.processTrackers();
+	this.processChanges(changes);
+};
+
+/*
+Add a tracker to the filter tracker
+filterString: the filter string to track
+fnEnter: function to call when a title enters the filter results. Called even if the tiddler does not actually exist. Called as (title), and should return a truthy value that is stored in the tracker as the "enterValue"
+fnLeave: function to call when a title leaves the filter results. Called as (title,enterValue)
+fnChange: function to call when a tiddler changes in the filter results. Only called for filter results that identify a tiddler or shadow tiddler. Called as (title,enterValue), and may optionally return a replacement enterValue
+*/
+FilterTracker.prototype.track = function(filterString,fnEnter,fnLeave,fnChange) {
+	// Add the tracker details
+	var index = this.trackers.length;
+	this.trackers.push({
+		filterString: filterString,
+		fnEnter: fnEnter,
+		fnLeave: fnLeave,
+		fnChange: fnChange,
+		previousResults: [], // Results from the previous time the tracker was processed
+		resultValues: {} // Map by title to the value returned by fnEnter
+	});
+	// Process the tracker
+	this.processTracker(index);
+};
+
+FilterTracker.prototype.processTrackers = function() {
+	for(var t=0; t<this.trackers.length; t++) {
+		this.processTracker(t);
+	}
+};
+
+FilterTracker.prototype.processTracker = function(index) {
+	var tracker = this.trackers[index],
+		results = this.wiki.filterTiddlers(tracker.filterString);
+	// Process the results
+	$tw.utils.each(results,function(title) {
+		if(tracker.previousResults.indexOf(title) === -1 && !tracker.resultValues[title]) {
+			tracker.resultValues[title] = tracker.fnEnter(title) || true;
+		}
+	});
+	$tw.utils.each(tracker.previousResults,function(title) {
+		if(results.indexOf(title) === -1 && tracker.resultValues[title]) {
+			tracker.fnLeave(title,tracker.resultValues[title]);
+			delete tracker.resultValues[title];
+		}
+	});
+	// Update the previous results
+	tracker.previousResults = results;
+};
+
+FilterTracker.prototype.processChanges = function(changes) {
+	for(var t=0; t<this.trackers.length; t++) {
+		var tracker = this.trackers[t];
+		$tw.utils.each(changes,function(change,title) {
+			if(tracker.previousResults.indexOf(title) !== -1) {
+				// Call the change function and if it doesn't return a value then keep the old value
+				tracker.resultValues[title] = tracker.fnChange(title,tracker.resultValues[title]) || tracker.resultValues[title];
+			}
+		});
+	}
+};
+
+exports.FilterTracker = FilterTracker;
+
+})();

core/modules/info/mediaquerytracker.js

@@ -13,36 +13,55 @@ Initialise $:/info/ tiddlers derived from media queries via
 "use strict";
 
 exports.getInfoTiddlerFields = function(updateInfoTiddlersCallback) {
-	var infoTiddlerFields = [];
 	if($tw.browser) {
-		// Get the media query tracker tiddlers
-		var trackers = $tw.wiki.getTiddlersWithTag("$:/tags/MediaQueryTracker");
-		$tw.utils.each(trackers,function(title) {
-			var tiddler = $tw.wiki.getTiddler(title);
+		// Functions to start and stop tracking a particular media query tracker tiddler
+		function track(title) {
+			var result = {},
+				tiddler = $tw.wiki.getTiddler(title);
 			if(tiddler) {
 				var mediaQuery = tiddler.fields["media-query"],
 					infoTiddler = tiddler.fields["info-tiddler"],
 					infoTiddlerAlt = tiddler.fields["info-tiddler-alt"];
 				if(mediaQuery && infoTiddler) {
 					// Evaluate and track the media query
-					var mqList = window.matchMedia(mediaQuery);
+					result.mqList = window.matchMedia(mediaQuery);
 					function getResultTiddlers() {
-						var value = mqList.matches ? "yes" : "no",
-							tiddlers = [{title: infoTiddler, text: value}];
+						var value = result.mqList.matches ? "yes" : "no",
+							tiddlers = [];
+						tiddlers.push({title: infoTiddler, text: value});
 						if(infoTiddlerAlt) {
 							tiddlers.push({title: infoTiddlerAlt, text: value})
 						}
 						return tiddlers;
 					};
-					infoTiddlerFields.push.apply(infoTiddlerFields,getResultTiddlers());
-					mqList.addEventListener("change",function(event) {
+					updateInfoTiddlersCallback(getResultTiddlers());
+					result.handler = function(event) {
 						updateInfoTiddlersCallback(getResultTiddlers());
-					});
+					};
+					result.mqList.addEventListener("change",result.handler);
 				}
 			}
-		});
+			return result;
+		}
+		function untrack(enterValue) {
+			if(enterValue.mqList && enterValue.handler) {
+				enterValue.mqList.removeEventListener("change",enterValue.handler);
+			}
+		}
+		// Track media query tracker tiddlers
+		function fnEnter(title) {
+			return track(title);
+		}
+		function fnLeave(title,enterValue) {
+			untrack(enterValue);
+		}
+		function fnChange(title,enterValue) {
+			untrack(enterValue);
+			return track(title);
+		}
+		$tw.filterTracker.track("[all[tiddlers+shadows]tag[$:/tags/MediaQueryTracker]!is[draft]]",fnEnter,fnLeave,fnChange);
 	}
-	return infoTiddlerFields;
+	return [];
 };
 
 })();

core/modules/startup/load-modules.js

@@ -16,6 +16,9 @@ Load core modules
 exports.name = "load-modules";
 exports.synchronous = true;
 
+// Set to `true` to enable performance instrumentation
+var PERFORMANCE_INSTRUMENTATION_CONFIG_TITLE = "$:/config/Performance/Instrumentation";
+
 exports.startup = function() {
 	// Load modules
 	$tw.modules.applyMethods("utils",$tw.utils);
@@ -35,6 +38,14 @@ exports.startup = function() {
 	$tw.macros = $tw.modules.getModulesByTypeAsHashmap("macro");
 	$tw.wiki.initParsers();
 	$tw.Commander.initCommands();
+	// --------------------------
+	// The rest of the startup process here is not strictly to do with loading modules, but are needed before other startup
+	// modules are executed. It is easier to put them here than to introduce a new startup module
+	// --------------------------
+	// Set up the performance framework
+	$tw.perf = new $tw.Performance($tw.wiki.getTiddlerText(PERFORMANCE_INSTRUMENTATION_CONFIG_TITLE,"no") === "yes");
+	// Kick off the filter tracker
+	$tw.filterTracker = new $tw.FilterTracker($tw.wiki);
 };
 
 })();

core/modules/startup/startup.js

@@ -17,9 +17,6 @@ exports.name = "startup";
 exports.after = ["load-modules"];
 exports.synchronous = true;
 
-// Set to `true` to enable performance instrumentation
-var PERFORMANCE_INSTRUMENTATION_CONFIG_TITLE = "$:/config/Performance/Instrumentation";
-
 var widget = require("$:/core/modules/widgets/widget.js");
 
 exports.startup = function() {
@@ -57,8 +54,6 @@ exports.startup = function() {
 	}
 	// Initialise version
 	$tw.version = $tw.utils.extractVersionInfo();
-	// Set up the performance framework
-	$tw.perf = new $tw.Performance($tw.wiki.getTiddlerText(PERFORMANCE_INSTRUMENTATION_CONFIG_TITLE,"no") === "yes");
 	// Create a root widget for attaching event handlers. By using it as the parentWidget for another widget tree, one can reuse the event handlers
 	$tw.rootWidget = new widget.widget({
 		type: "widget",

editions/tw5.com/tiddlers/mechanisms/InfoMechanism.tid

@@ -19,8 +19,8 @@ System tiddlers in the namespace `$:/info/` are used to expose information about
 |[[$:/info/browser/language]] |<<.from-version "5.1.20">> Language as reported by browser (note that some browsers report two character codes such as `en` while others report full codes such as `en-GB`) |
 |[[$:/info/browser/screen/width]] |Screen width in pixels |
 |[[$:/info/browser/screen/height]] |Screen height in pixels |
-|[[$:/info/browser/darkmode]] |<<.from-version "5.3.6">> Is dark mode preferred? ("yes" or "no") |
-|[[$:/info/darkmode]] |<<.deprecated-since "5.3.6">> Alias for  $:/info/browser/darkmode |
+|[[$:/info/browser/darkmode]] |<<.from-version "5.3.7">> Is dark mode preferred? ("yes" or "no") |
+|[[$:/info/darkmode]] |<<.deprecated-since "5.3.7">> Alias for  $:/info/browser/darkmode |
 |[[$:/info/node]] |Running under [[Node.js]]? ("yes" or "no") |
 |[[$:/info/url/full]] |<<.from-version "5.1.14">> Full URL of wiki (eg, ''<<example full>>'') |
 |[[$:/info/url/host]] |<<.from-version "5.1.14">> Host portion of URL of wiki (eg, ''<<example host>>'') |

editions/tw5.com/tiddlers/mechanisms/MediaQueryTrackerMechanism.tid

@@ -1,8 +1,8 @@
 title: MediaQueryTrackerMechanism
 tags: Mechanisms
 
-The media query tracker mechanism allows you to define [[custom CSS media queries|https://developer.mozilla.org/en-US/docs/Web/CSS/CSS_media_queries/Using_media_queries]] to be bound to a specified [[info|InfoMechanism]] tiddler. The info tiddler will be dynamically update to reflect the current state of the media query.
+<<.from-version "5.3.7">> The media query tracker mechanism allows you to define [[custom CSS media queries|https://developer.mozilla.org/en-US/docs/Web/CSS/CSS_media_queries/Using_media_queries]] to be bound to a specified [[info|InfoMechanism]] tiddler. The info tiddler will be dynamically update to reflect the current state of the media query.
 
-Adding or modifying a tiddler tagged $:/tags/MediaQueryTracker will only take effect when the wiki is reloaded
+Adding or modifying a tiddler tagged $:/tags/MediaQueryTracker takes effect immediately.
 
 The media queries are always applied against the main window. This is relevant for viewport related media queries such as `min-width` which will always respect the main window and ignore the sizes of any external windows.