Index: ps/trunk/binaries/data/mods/public/simulation/ai/common-api/gamestate.js
===================================================================
--- ps/trunk/binaries/data/mods/public/simulation/ai/common-api/gamestate.js
+++ ps/trunk/binaries/data/mods/public/simulation/ai/common-api/gamestate.js
@@ -225,7 +225,7 @@
 /** true if started or queued */
 m.GameState.prototype.isResearching = function(template)
 {
-	return this.playerData.researchStarted[template] !== undefined ||
+	return this.playerData.researchStarted.has(template) ||
 	       this.playerData.researchQueued[template] !== undefined;
 };
 
@@ -241,7 +241,7 @@
 
 	// researching or already researched: NOO.
 	if (this.playerData.researchQueued[techTemplateName] ||
-	    this.playerData.researchStarted[techTemplateName] ||
+	    this.playerData.researchStarted.has(techTemplateName) ||
 	    this.playerData.researchedTechs.has(techTemplateName))
 		return false;
 
@@ -253,7 +253,7 @@
 	{
 		let other = template.pairedWith();
 		if (this.playerData.researchQueued[other] ||
-		    this.playerData.researchStarted[other] ||
+		    this.playerData.researchStarted.has(other) ||
 		    this.playerData.researchedTechs.has(other))
 			return false;
 	}
Index: ps/trunk/binaries/data/mods/public/simulation/components/GuiInterface.js
===================================================================
--- ps/trunk/binaries/data/mods/public/simulation/components/GuiInterface.js
+++ ps/trunk/binaries/data/mods/public/simulation/components/GuiInterface.js
@@ -704,7 +704,7 @@
 		return {};
 
 	let ret = {};
-	for (let tech in cmpTechnologyManager.GetStartedTechs())
+	for (let tech of cmpTechnologyManager.GetStartedTechs())
 	{
 		ret[tech] = { "researcher": cmpTechnologyManager.GetResearcher(tech) };
 		let cmpProductionQueue = Engine.QueryInterface(ret[tech].researcher, IID_ProductionQueue);
Index: ps/trunk/binaries/data/mods/public/simulation/components/TechnologyManager.js
===================================================================
--- ps/trunk/binaries/data/mods/public/simulation/components/TechnologyManager.js
+++ ps/trunk/binaries/data/mods/public/simulation/components/TechnologyManager.js
@@ -24,7 +24,9 @@
 	this.researchedTechs = new Set();
 
 	this.researchQueued = {};  // technologies which are queued for research
-	this.researchStarted = {}; // technologies which are being researched currently (non-queued)
+
+	// technologies which are being researched currently (non-queued)
+	this.researchStarted = new Set();
 
 	// This stores the modifications to unit stats from researched technologies
 	// Example data: {"ResourceGatherer/Rates/food.grain": [
@@ -101,7 +103,7 @@
 
 TechnologyManager.prototype.IsTechnologyStarted = function(tech)
 {
-	return this.researchStarted[tech] !== undefined;
+	return this.researchStarted.has(tech);
 };
 
 // Checks the requirements for a technology to see if it can be researched at the current time
@@ -400,7 +402,7 @@
 // Marks a technology as actively being researched
 TechnologyManager.prototype.StartedResearch = function(tech, notification)
 {
-	this.researchStarted[tech] = true;
+	this.researchStarted.add(tech);
 
 	if (notification && tech.startsWith("phase"))
 	{
@@ -418,7 +420,7 @@
 // Marks a technology as not being currently researched
 TechnologyManager.prototype.StoppedResearch = function(tech, notification)
 {
-	if (notification && tech.startsWith("phase") && this.researchStarted[tech])
+	if (notification && tech.startsWith("phase") && this.researchStarted.has(tech))
 	{
 		let cmpPlayer = Engine.QueryInterface(this.entity, IID_Player);
 		let cmpGUIInterface = Engine.QueryInterface(SYSTEM_ENTITY, IID_GuiInterface);
@@ -431,7 +433,7 @@
 	}
 
 	delete this.researchQueued[tech];
-	delete this.researchStarted[tech];
+	this.researchStarted.delete(tech);
 };
 
 // Checks whether a technology is set to be researched
@@ -443,7 +445,9 @@
 		return false;
 };
 
-// Get all techs that are currently being researched
+/**
+ * Returns the names of technologies that are currently being researched (non-queued).
+ */
 TechnologyManager.prototype.GetStartedTechs = function()
 {
 	return this.researchStarted;
Index: ps/trunk/binaries/data/mods/public/simulation/components/tests/test_GuiInterface.js
===================================================================
--- ps/trunk/binaries/data/mods/public/simulation/components/tests/test_GuiInterface.js
+++ ps/trunk/binaries/data/mods/public/simulation/components/tests/test_GuiInterface.js
@@ -126,7 +126,7 @@
 AddMock(100, IID_TechnologyManager, {
 	IsTechnologyResearched: function(tech) { if (tech == "phase_village") return true; else return false; },
 	GetQueuedResearch: function() { return {}; },
-	GetStartedTechs: function() { return {}; },
+	GetStartedTechs: function() { return new Set(); },
 	GetResearchedTechs: function() { return {}; },
 	GetClassCounts: function() { return {}; },
 	GetTypeCountsByClass: function() { return {}; },
@@ -212,7 +212,7 @@
 AddMock(101, IID_TechnologyManager, {
 		IsTechnologyResearched: function(tech) { if (tech == "phase_village") return true; else return false; },
 		GetQueuedResearch: function() { return {}; },
-		GetStartedTechs: function() { return {}; },
+		GetStartedTechs: function() { return new Set(); },
 		GetResearchedTechs: function() { return {}; },
 		GetClassCounts: function() { return {}; },
 		GetTypeCountsByClass: function() { return {}; },
@@ -296,7 +296,7 @@
 			entityCounts: {"Foo": 5},
 			entityLimitChangers: {"Foo": {}},
 			researchQueued: {},
-			researchStarted: {},
+			researchStarted: new Set(),
 			researchedTechs: new Set(),
 			classCounts: {},
 			typeCountsByClass: {},
@@ -345,7 +345,7 @@
 			entityCounts: {"Bar": 0},
 			entityLimitChangers: {"Bar": {}},
 			researchQueued: {},
-			researchStarted: {},
+			researchStarted: new Set(),
 			researchedTechs: new Set(),
 			classCounts: {},
 			typeCountsByClass: {},
@@ -403,7 +403,7 @@
 			"entityCounts": {"Foo": 5},
 			"entityLimitChangers": {"Foo": {}},
 			"researchQueued": {},
-			"researchStarted": {},
+			"researchStarted": new Set(),
 			"researchedTechs": new Set(),
 			"classCounts": {},
 			"typeCountsByClass": {},
@@ -475,7 +475,7 @@
 			"entityCounts": {"Bar": 0},
 			"entityLimitChangers": {"Bar": {}},
 			"researchQueued": {},
-			"researchStarted": {},
+			"researchStarted": new Set(),
 			"researchedTechs": new Set(),
 			"classCounts": {},
 			"typeCountsByClass": {},