diff --git a/src/codec.js b/src/codec.js
new file mode 100644
index 0000000..d15cfdd
--- /dev/null
+++ b/src/codec.js
@@ -0,0 +1,33 @@
+// Wire protocol representation of events and actions
+
+var Route = require("./route.js");
+
+function _encode(e) {
+    switch (e.type) {
+    case "routes":
+	return ["routes", e.gestalt.serialize(function (v) { return true; })];
+    case "message":
+	return ["message", e.message, e.metaLevel, e.isFeedback];
+    }
+}
+
+function _decode(what) {
+  return function (j) {
+    switch (j[0]) {
+    case "routes":
+      return Minimart.updateRoutes([
+	Route.deserializeGestalt(j[1], function (v) { return true; })]);
+    case "message":
+      return Minimart.sendMessage(j[1], j[2], j[3]);
+    default:
+      throw { message: "Invalid JSON-encoded " + what + ": " + JSON.stringify(j) };
+    }
+  };
+}
+
+///////////////////////////////////////////////////////////////////////////
+
+module.exports.encodeEvent = _encode;
+module.exports.decodeEvent = _decode("event");
+module.exports.encodeAction = _encode;
+module.exports.decodeAction = _decode("action");
diff --git a/src/ground.js b/src/ground.js
new file mode 100644
index 0000000..c1839d9
--- /dev/null
+++ b/src/ground.js
@@ -0,0 +1,61 @@
+/* Ground interface */
+var Minimart = require("./minimart.js");
+var World = Minimart.World;
+
+function Ground(bootFn) {
+    var self = this;
+    this.stepperId = null;
+    World.withWorldStack([[this, -1]], function () {
+	self.world = new World(bootFn);
+    });
+}
+
+Ground.prototype.step = function () {
+    var self = this;
+    return World.withWorldStack([[this, -1]], function () {
+	return self.world.step();
+    });
+};
+
+Ground.prototype.checkPid = function (pid) {
+    if (pid !== -1) console.error("Weird pid in Ground markPidRunnable", pid);
+};
+
+Ground.prototype.markPidRunnable = function (pid) {
+    this.checkPid(pid);
+    this.startStepping();
+};
+
+Ground.prototype.startStepping = function () {
+    var self = this;
+    if (this.stepperId) return;
+    if (this.step()) {
+	this.stepperId = setTimeout(function () {
+	    self.stepperId = null;
+	    self.startStepping();
+	}, 0);
+    }
+};
+
+Ground.prototype.stopStepping = function () {
+    if (this.stepperId) {
+	clearTimeout(this.stepperId);
+	this.stepperId = null;
+    }
+};
+
+Ground.prototype.enqueueAction = function (pid, action) {
+    this.checkPid(pid);
+    if (action.type === 'routes') {
+	if (!action.gestalt.isEmpty()) {
+	    console.error("You have subscribed to a nonexistent event source.",
+			  action.gestalt.pretty());
+	}
+    } else {
+	console.error("You have sent a message into the outer void.", action);
+    }
+};
+
+///////////////////////////////////////////////////////////////////////////
+
+module.exports.Ground = Ground;
diff --git a/src/main.js b/src/main.js
index 06c1468..f957905 100644
--- a/src/main.js
+++ b/src/main.js
@@ -6,6 +6,7 @@ module.exports.RoutingTableWidget = require("./routing-table-widget.js");
 module.exports.WebSocket = require("./websocket-driver.js");
 module.exports.Reflect = require("./reflect.js");
 
+module.exports.Ground = require("./ground.js").Ground;
+module.exports.Actor = require("./actor.js").Actor;
 module.exports.Spy = require("./spy.js").Spy;
 module.exports.WakeDetector = require("./wake-detector.js").WakeDetector;
-module.exports.Actor = require("./actor.js").Actor;
diff --git a/src/minimart.js b/src/minimart.js
index dd6c9fc..c7cad5f 100644
--- a/src/minimart.js
+++ b/src/minimart.js
@@ -1,4 +1,5 @@
 var Route = require("./route.js");
+var Util = require("./util.js");
 
 ///////////////////////////////////////////////////////////////////////////
 
@@ -390,7 +391,7 @@ World.prototype.clearTombstones = function () {
 /* Utilities: matching demand for some service */
 
 function DemandMatcher(projection, metaLevel, options) {
-    options = $.extend({
+    options = Util.extend({
 	demandLevel: 0,
 	supplyLevel: 0,
 	demandSideIsSubscription: false
@@ -481,63 +482,6 @@ Deduplicator.prototype.expireMessages = function () {
     }
 };
 
-/*---------------------------------------------------------------------------*/
-/* Ground interface */
-
-function Ground(bootFn) {
-    var self = this;
-    this.stepperId = null;
-    World.withWorldStack([[this, -1]], function () {
-	self.world = new World(bootFn);
-    });
-}
-
-Ground.prototype.step = function () {
-    var self = this;
-    return World.withWorldStack([[this, -1]], function () {
-	return self.world.step();
-    });
-};
-
-Ground.prototype.checkPid = function (pid) {
-    if (pid !== -1) console.error("Weird pid in Ground markPidRunnable", pid);
-};    
-
-Ground.prototype.markPidRunnable = function (pid) {
-    this.checkPid(pid);
-    this.startStepping();
-};
-
-Ground.prototype.startStepping = function () {
-    var self = this;
-    if (this.stepperId) return;
-    if (this.step()) {
-	this.stepperId = setTimeout(function () {
-	    self.stepperId = null;
-	    self.startStepping();
-	}, 0);
-    }
-};
-
-Ground.prototype.stopStepping = function () {
-    if (this.stepperId) {
-	clearTimeout(this.stepperId);
-	this.stepperId = null;
-    }
-};
-
-Ground.prototype.enqueueAction = function (pid, action) {
-    this.checkPid(pid);
-    if (action.type === 'routes') {
-	if (!action.gestalt.isEmpty()) {
-	    console.error("You have subscribed to a nonexistent event source.",
-			  action.gestalt.pretty());
-	}
-    } else {
-	console.error("You have sent a message into the outer void.", action);
-    }
-};
-
 ///////////////////////////////////////////////////////////////////////////
 
 module.exports.__ = __;
@@ -553,5 +497,4 @@ module.exports.shutdownWorld = shutdownWorld;
 module.exports.World = World;
 module.exports.DemandMatcher = DemandMatcher;
 module.exports.Deduplicator = Deduplicator;
-module.exports.Ground = Ground;
 module.exports.Route = Route;
diff --git a/src/util.js b/src/util.js
new file mode 100644
index 0000000..3b20f3b
--- /dev/null
+++ b/src/util.js
@@ -0,0 +1,13 @@
+// Minimal jQueryish utilities. Reimplemented because jQuery needs
+// window to exist, and we want to run in Web Worker context as well.
+
+function extend(what, _with) {
+  for (var prop in _with) {
+    if (_with.hasOwnProperty(prop)) {
+      what[prop] = _with[prop];
+    }
+  }
+  return what;
+}
+
+module.exports.extend = extend;
diff --git a/src/websocket-driver.js b/src/websocket-driver.js
index 765c9f4..1120d72 100644
--- a/src/websocket-driver.js
+++ b/src/websocket-driver.js
@@ -1,4 +1,5 @@
 var Minimart = require("./minimart.js");
+var Codec = require("./codec.js");
 var Route = Minimart.Route;
 var World = Minimart.World;
 var sub = Minimart.sub;
@@ -97,7 +98,7 @@ WebSocketConnection.prototype.safeSend = function (m) {
 
 WebSocketConnection.prototype.sendLocalRoutes = function () {
     var newLocalRoutesMessage =
-	JSON.stringify(encodeEvent(Minimart.updateRoutes([this.localGestalt])));
+	JSON.stringify(Codec.encodeEvent(Minimart.updateRoutes([this.localGestalt])));
     if (this.prevLocalRoutesMessage !== newLocalRoutesMessage) {
 	this.prevLocalRoutesMessage = newLocalRoutesMessage;
 	this.safeSend(newLocalRoutesMessage);
@@ -138,7 +139,7 @@ WebSocketConnection.prototype.handleEvent = function (e) {
 	var m = e.message;
 	if (m.length && m.length === 3 && m[0] === this.label)
 	{
-	    var encoded = JSON.stringify(encodeEvent(
+	    var encoded = JSON.stringify(Codec.encodeEvent(
 		Minimart.sendMessage(m[2], m[1], e.isFeedback)));
 	    if (this.deduplicator.accept(encoded)) {
 		this.safeSend(encoded);
@@ -227,32 +228,6 @@ WebSocketConnection.prototype.onclose = function (e) {
     }
 };
 
-///////////////////////////////////////////////////////////////////////////
-// Wire protocol representation of events and actions
-
-function encodeEvent(e) {
-    switch (e.type) {
-    case "routes":
-	return ["routes", e.gestalt.serialize(function (v) { return true; })];
-    case "message":
-	return ["message", e.message, e.metaLevel, e.isFeedback];
-    }
-}
-
-function decodeAction(j) {
-    switch (j[0]) {
-    case "routes":
-	return Minimart.updateRoutes([
-	    Route.deserializeGestalt(j[1], function (v) { return true; })]);
-    case "message":
-	return Minimart.sendMessage(j[1], j[2], j[3]);
-    default:
-	throw { message: "Invalid JSON-encoded action: " + JSON.stringify(j) };
-    }
-}
-
 ///////////////////////////////////////////////////////////////////////////
 
 module.exports.WebSocketConnection = WebSocketConnection;
-module.exports.encodeEvent = encodeEvent;
-module.exports.decodeAction = decodeAction;