diff --git a/lib/assert.js b/lib/assert.js
new file mode 100644
index 00000000..1b769472
--- /dev/null
+++ b/lib/assert.js
@@ -0,0 +1,6 @@
+this.assert = function(condition, message) {
+  if (!condition) {
+    console.error(message);
+    throw new Error;
+  }
+}
diff --git a/lib/stroke_extractor.js b/lib/stroke_extractor.js
index a933c475..355ac20a 100644
--- a/lib/stroke_extractor.js
+++ b/lib/stroke_extractor.js
@@ -3,14 +3,6 @@ var MIN_CORNER_ANGLE = 0.1*Math.PI;
 var MIN_CORNER_TANGENT_DISTANCE = 4;
 var REVERSAL_PENALTY = 0.5;
 
-// Error out if the condition does not hold.
-function assert(condition, message) {
-  if (!condition) {
-    console.error(message);
-    throw new Error;
-  }
-}
-
 // Helper methods for use with angles, which are floats in [-pi, pi).
 var Angle = {
   subtract: function(angle1, angle2) {
@@ -28,7 +20,7 @@ var Angle = {
   },
 };
 
-// Helper methods for use with "points", which are just pairs of integers.
+// Helper methods for use with "points", which are pairs of integers.
 var Point = {
   angle: function(point) {
     return Math.atan2(point[1], point[0]);
diff --git a/server/migration.js b/server/migration.js
index a0933af4..f3825131 100644
--- a/server/migration.js
+++ b/server/migration.js
@@ -1,10 +1,3 @@
-function assert(condition, message) {
-  if (!condition) {
-    console.log(message);
-    throw new Error;
-  }
-}
-
 function get_final_bridges(glyph, original_bridges) {
   var set = {};
   var result = original_bridges.concat(glyph.manual.bridges_added);