From ad89efe5926f2e261bb0dc0cd1cfe690f74571b2 Mon Sep 17 00:00:00 2001
From: Chad Hietala <chadhietala@gmail.com>
Date: Wed, 7 Oct 2015 11:57:22 -0700
Subject: [PATCH] [PERF] Don't Attempt To Sanitive Unsanitizeable

This adds an identity check for falsy values before the value is
sanitized. Currently we do work to sanitize things like `undefined`.
---
 packages/morph-attr/lib/main.js              |  2 +-
 packages/morph-attr/tests/attr-morph-test.js | 14 ++++++++++++++
 2 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/packages/morph-attr/lib/main.js b/packages/morph-attr/lib/main.js
index 48f39332..792b3120 100644
--- a/packages/morph-attr/lib/main.js
+++ b/packages/morph-attr/lib/main.js
@@ -110,7 +110,7 @@ AttrMorph.prototype.setContent = function (value) {
   if (this.lastValue === value) { return; }
   this.lastValue = value;
 
-  if (this.escaped) {
+  if (this.escaped && value) {
     var sanitized = sanitizeAttributeValue(this.domHelper, this.element, this.attrName, value);
     this._update(sanitized, this.namespace);
   } else {
diff --git a/packages/morph-attr/tests/attr-morph-test.js b/packages/morph-attr/tests/attr-morph-test.js
index 7284f5b2..34db1983 100644
--- a/packages/morph-attr/tests/attr-morph-test.js
+++ b/packages/morph-attr/tests/attr-morph-test.js
@@ -17,6 +17,20 @@ test("can update a dom node", function(){
   equal(element.getAttribute('id'), 'twang', 'id attribute is set');
 });
 
+test("setting content to undefined calls _update with undefiend", function(){
+  var element = domHelper.createElement('div');
+  var morph = domHelper.createAttrMorph(element, 'id');
+  var update = morph._setContent;
+  var calledWith;
+  morph.setContent(undefined);
+  morph._update = function(value) {
+    calledWith = value;
+    return update.apply(morph, arguments);
+  };
+  ok(calledWith === undefined);
+  equal(element.id, '');
+});
+
 test("can clear", function(){
   expect(0);
   var element = domHelper.createElement('div');