diff --git a/js-assembler/runtime-src/baselib-functions.js b/js-assembler/runtime-src/baselib-functions.js
index 4f4fce0..86b6b3e 100644
--- a/js-assembler/runtime-src/baselib-functions.js
+++ b/js-assembler/runtime-src/baselib-functions.js
@@ -85,39 +85,6 @@
     };
 
 
-    var coersePrimitiveToJavaScript = function (v, MACHINE) {
-        return function (succ, fail) {
-            try {
-                succ = succ || function () {};
-                fail = fail || function () {};
-
-                var oldArgcount = MACHINE.a, i;
-                MACHINE.a = arguments.length - 2;
-                for (i = 0; i < arguments.length - 2; i++) {
-                    MACHINE.e.push(arguments[arguments.length - 1 - i]);
-                }
-
-                if (!(baselib.arity.isArityMatching(v.racketArity, MACHINE.a))) {
-                    var msg = baselib.format.format("arity mismatch: ~s expected ~s arguments, but received ~s",
-                                                    [v.displayName, v.racketArity, MACHINE.a]);
-                    return fail(new baselib.exceptions.RacketError(
-                        msg,
-                        baselib.exceptions.makeExnFailContractArity(msg,
-                                                                    MACHINE.captureContinuationMarks())));
-                }
-
-                var result = v(MACHINE);
-                MACHINE.a = oldArgcount;
-                for (i = 0; i < arguments.length - 2; i++) { 
-                    MACHINE.e.pop();
-                }
-                succ(result);
-            } catch (e) {
-                fail(e);
-            }
-        };
-    };
-
     var coerseClosureToJavaScript = function (v, MACHINE) {
         var f = function (succ, fail) {
             var args = [];
diff --git a/js/world/js-impl.js b/js/world/js-impl.js
index 243e911..1bc2f9a 100644
--- a/js/world/js-impl.js
+++ b/js/world/js-impl.js
@@ -20,52 +20,53 @@
      * Creates an event source coupled to a JavaScript function.  Calling the function
      * should cause the event source to fire.
      */
-    var makeJsEventSource = function() {
+    var makeJsEventSource = function(startupProcedure, shutdownProcedure) {
         var enabled = false;
         var fireEvent;
 
-        var JsEventSource = function() {};
-        JsEventSource.prototype = plt.baselib.heir(EventSource.prototype);
-        JsEventSource.prototype.onStart = function(_fireEvent) {
-            enabled = true;
-            fireEvent = _fireEvent;
-        };
-        JsEventSource.prototype.onStop = function() {
-            enabled = false;
-            fireEvent = void(0);
-        };
-
         var sender = function(v) {
             if (enabled) {
                 fireEvent(void(0), v);
             }
         };
-        return { eventSource: new JsEventSource(),
-                 sender: sender };
+
+        var JsEventSource = function() {
+            this.startupData = void(0);
+        };
+        JsEventSource.prototype = plt.baselib.heir(EventSource.prototype);
+        JsEventSource.prototype.onStart = function(_fireEvent) {
+            this.startupData = startupProcedure(sender);
+            enabled = true;
+            fireEvent = _fireEvent;
+        };
+        JsEventSource.prototype.onStop = function() {
+            shutdownProcedure(sender, this.startupData);
+            enabled = false;
+            fireEvent = void(0);
+        };
+
+        return new JsEventSource();
     };
 
 
-    var makeJsWorldEvent = makeClosure(
-        'make-js-world-event',
-        0,
+    var makeWorldEventHandler = makeClosure(
+        'make-world-event-handler',
+        2,
         function(M) {
-            var eventSourceRecord = makeJsEventSource();
-            eventSourceRecord.eventSource
+            var setupProcedure = checkProcedure(M, 'make-world-event-handler', 0);
+            var shutdownProcedure = checkProcedure(M, 'make-world-event-handler', 1);
+            var eventSource = makeJsEventSource(setupProcedure, shutdownProcedure);
             var makeHandler = makePrimitiveProcedure(
                 'make-js-world-event',
                 1,
                 function(M) {
                     var onEvent = wrapFunction(checkProcedure(M, 'js-world-event-handler', 0));
-                    return new EventHandler('js-world-event',
-                                            eventSourceRecord.eventSource,
-                                            onEvent);
+                    return new EventHandler('js-world-event', eventSource, onEvent);
                 });
-            finalizeClosureCall(M,
-                                makeHandler, 
-                                eventSourceRecord.sender);
+            finalizeClosureCall(M, makeHandler);
         });
 
 
-    EXPORTS['make-js-world-event'] = makeJsWorldEvent;
+    EXPORTS['make-world-event-handler'] = makeWorldEventHandler;
 
 }());
\ No newline at end of file
diff --git a/js/world/main.rkt b/js/world/main.rkt
index 723aa39..7be3db5 100644
--- a/js/world/main.rkt
+++ b/js/world/main.rkt
@@ -1,3 +1,3 @@
 #lang s-exp "../../lang/base.rkt"
-(require "make-js-world-event.rkt")
-(provide (all-from-out "make-js-world-event.rkt"))
+(require "world-event-handler.rkt")
+(provide (all-from-out "world-event-handler.rkt"))
diff --git a/js/world/racket-impl.rkt b/js/world/racket-impl.rkt
index 253e4ed..3262150 100644
--- a/js/world/racket-impl.rkt
+++ b/js/world/racket-impl.rkt
@@ -2,5 +2,5 @@
 
 (provide make-js-world-event)
 
-(define (make-js-world-event)
-  (error 'make-js-world-event "Must be run under a JavaScript context."))
+(define (make-world-event-handler setup shutdown)
+  (error 'make-world-event-handler "Must be run under a JavaScript context."))
diff --git a/js/world/make-js-world-event.rkt b/js/world/world-event-handler.rkt
similarity index 76%
rename from js/world/make-js-world-event.rkt
rename to js/world/world-event-handler.rkt
index b2d0733..aeef438 100644
--- a/js/world/make-js-world-event.rkt
+++ b/js/world/world-event-handler.rkt
@@ -3,4 +3,4 @@
 (declare-implementation
  #:racket "racket-impl.rkt"
  #:javascript ("js-impl.js")
- #:provided-values (make-js-world-event))
\ No newline at end of file
+ #:provided-values (make-world-event-handler))
\ No newline at end of file
diff --git a/web-world/geolocation.rkt b/web-world/geolocation.rkt
new file mode 100644
index 0000000..4b6c94d
--- /dev/null
+++ b/web-world/geolocation.rkt
@@ -0,0 +1,17 @@
+#lang s-exp "../lang/base.rkt"
+(require "../js/world.rkt"
+         "../js.rkt")
+
+;; Create a new event handler type
+(define-values (on-geo-change locationCallback)
+  (make-js-event-type))
+
+(define start-up-geo
+  (js-function->procedure
+   "function(locationCallback) {
+        navigator.geolocation.watchPosition(
+            function(evt) { locationCallback(evt.latitude, evt.longitude); })}"))
+
+;; TODO: adjust the FFI so we can start-up and shutdown this more easily.
+(start-up-geo locationCallback)
+