diff --git a/lib/assets/javascripts/flowerbox.js.coffee b/lib/assets/javascripts/flowerbox.js.coffee
index ee4ec8c..fd574d0 100644
--- a/lib/assets/javascripts/flowerbox.js.coffee
+++ b/lib/assets/javascripts/flowerbox.js.coffee
@@ -21,7 +21,11 @@ Flowerbox =
           message = Flowerbox.messageQueue.shift()
           Flowerbox.socket.send(JSON.stringify(message))
 
-    Flowerbox.done = true if url == 'results'
+    if url == 'results'
+      if __$instrument?
+        Flowerbox.socket.send(JSON.stringify(['instrument', __$instrument]))
+
+      Flowerbox.done = true
 
   started: false
   done: false
diff --git a/lib/flowerbox/configuration.rb b/lib/flowerbox/configuration.rb
index d1f56e4..ea97dff 100644
--- a/lib/flowerbox/configuration.rb
+++ b/lib/flowerbox/configuration.rb
@@ -1,8 +1,9 @@
 require 'flowerbox/reporter_list'
+require 'flowerbox/instrumented_files_list'
 
 module Flowerbox
   class Configuration
-    attr_writer :reporters, :backtrace_filter
+    attr_writer :reporters, :backtrace_filter, :instrument_js
     attr_accessor :port
 
     attr_accessor :test_environment, :runner_environment, :bare_coffeescript
@@ -27,6 +28,14 @@ module Flowerbox
       @backtrace_filter ||= []
     end
 
+    def instrument_files
+      @instrument_files ||= Flowerbox::InstrumentedFilesList.new
+    end
+
+    def instrument_js?
+      !@instrument_files.empty?
+    end
+
     def test_with(what)
       self.test_environment = Flowerbox::TestEnvironment.for(what)
     end
diff --git a/lib/flowerbox/instrumented_files_list.rb b/lib/flowerbox/instrumented_files_list.rb
new file mode 100644
index 0000000..0f1fd2f
--- /dev/null
+++ b/lib/flowerbox/instrumented_files_list.rb
@@ -0,0 +1,22 @@
+require 'forwardable'
+
+module Flowerbox
+  class InstrumentedFilesList
+    extend Forwardable
+
+    def_delegators :@files_list, :empty?
+
+    def initialize
+      @files_list = []
+    end
+
+    def <<(pattern)
+      @files_list << pattern
+    end
+
+    def include?(filename)
+      @files_list.any? { |pattern| filename[pattern] }
+    end
+  end
+end
+
diff --git a/lib/flowerbox/runner/base.rb b/lib/flowerbox/runner/base.rb
index efde11e..0a22420 100644
--- a/lib/flowerbox/runner/base.rb
+++ b/lib/flowerbox/runner/base.rb
@@ -36,6 +36,9 @@ module Flowerbox
         sprockets.find_asset(file.first, :bundle => false).body
       end
 
+      def instrument(data)
+      end
+
       def ensure_alive
         while @count < MAX_COUNT && !finished?
           @count += 1 if @timer_running
@@ -92,8 +95,13 @@ module Flowerbox
         end
 
         @results
-      rescue ExecJS::RuntimeError => e
-        handle_coffeescript_compilation_error(e)
+      rescue => e
+        case e
+        when ExecJS::RuntimeError, ExecJS::ProgramError
+          handle_coffeescript_compilation_error(e)
+        else
+          raise e
+        end
       end
 
       def configured?
diff --git a/lib/flowerbox/sprockets_handler.rb b/lib/flowerbox/sprockets_handler.rb
index 98003f6..f4e25c5 100644
--- a/lib/flowerbox/sprockets_handler.rb
+++ b/lib/flowerbox/sprockets_handler.rb
@@ -40,6 +40,12 @@ module Flowerbox
       @environment = Sprockets::Environment.new
       @environment.cache = cache
 
+      if Flowerbox.instrument_js?
+        require 'flowerbox/tilt/instrument_js'
+
+        @environment.register_postprocessor 'application/javascript', Flowerbox::Tilt::InstrumentJS
+      end
+
       default_asset_paths.each { |path| @environment.append_path(path) }
 
       @environment
diff --git a/lib/flowerbox/tilt/instrument_js.rb b/lib/flowerbox/tilt/instrument_js.rb
new file mode 100644
index 0000000..0199c5b
--- /dev/null
+++ b/lib/flowerbox/tilt/instrument_js.rb
@@ -0,0 +1,42 @@
+require 'tilt'
+
+module Flowerbox
+  module Tilt
+    class InstrumentJS < ::Tilt::Template
+      def prepare ; end
+
+      def evaluate(scope, locals, &block)
+        if Flowerbox.instrument_files.include?(file)
+          block_comment = false
+
+          lines = data.lines.to_a
+
+          output = [
+            'if (typeof __$instrument == "undefined") { __$instrument = {} }',
+            "__$instrument['#{file}'] = [];",
+            "__$instrument['#{file}'][#{lines.length - 1}] = 0;"
+          ]
+
+          prior_comma_end = comma_end = false
+
+          lines.each_with_index do |line, index|
+            line.rstrip!
+
+            instrument = "__$instrument['#{file}'][#{index}] = 1;"
+
+            if line[%r{; *$}]
+              line = line + instrument
+            end
+
+            output << line
+          end
+
+          output.join("\n")
+        else
+          data
+        end
+      end
+    end
+  end
+end
+