From 22a43cff4d6c5a16a32696fef97e354eb5c33615 Mon Sep 17 00:00:00 2001
From: Kristiyan Kostadinov <crisbeto@abv.bg>
Date: Wed, 23 Jan 2019 18:41:20 +0100
Subject: [PATCH] fix(ivy): error when encountering an empty class attribute
 (#28321)

Fixes Ivy throwing an error if it encounters an empty class attribute in a template (`class=""`).

This PR resolves FW-972.

PR Close #28321
---
 .../styling/class_and_style_bindings.ts       | 19 +++++++++++--------
 .../linker/regression_integration_spec.ts     |  7 +++++++
 2 files changed, 18 insertions(+), 8 deletions(-)

diff --git a/packages/core/src/render3/styling/class_and_style_bindings.ts b/packages/core/src/render3/styling/class_and_style_bindings.ts
index a22b096772..e1d5325ea9 100644
--- a/packages/core/src/render3/styling/class_and_style_bindings.ts
+++ b/packages/core/src/render3/styling/class_and_style_bindings.ts
@@ -982,14 +982,17 @@ function setClass(
     if (playerBuilder) {
       playerBuilder.setValue(className, add);
     }
-  } else if (add) {
-    ngDevMode && ngDevMode.rendererAddClass++;
-    isProceduralRenderer(renderer) ? renderer.addClass(native, className) :
-                                     native['classList'].add(className);
-  } else {
-    ngDevMode && ngDevMode.rendererRemoveClass++;
-    isProceduralRenderer(renderer) ? renderer.removeClass(native, className) :
-                                     native['classList'].remove(className);
+    // DOMTokenList will throw if we try to add or remove an empty string.
+  } else if (className !== '') {
+    if (add) {
+      ngDevMode && ngDevMode.rendererAddClass++;
+      isProceduralRenderer(renderer) ? renderer.addClass(native, className) :
+                                       native['classList'].add(className);
+    } else {
+      ngDevMode && ngDevMode.rendererRemoveClass++;
+      isProceduralRenderer(renderer) ? renderer.removeClass(native, className) :
+                                       native['classList'].remove(className);
+    }
   }
 }
 
diff --git a/packages/core/test/linker/regression_integration_spec.ts b/packages/core/test/linker/regression_integration_spec.ts
index 5deff6ad2e..e46ba87c19 100644
--- a/packages/core/test/linker/regression_integration_spec.ts
+++ b/packages/core/test/linker/regression_integration_spec.ts
@@ -317,6 +317,13 @@ function declareTests(config?: {useJit: boolean}) {
       expect(ctx.componentInstance.viewContainers.first).toBe(vc);
     });
 
+    it('should not throw when encountering an empty class attribute', () => {
+      const template = '<div class=""></div>';
+      TestBed.overrideComponent(MyComp1, {set: {template}});
+
+      expect(() => TestBed.createComponent(MyComp1)).not.toThrow();
+    });
+
     describe('empty templates - #15143', () => {
       it('should allow empty components', () => {
         @Component({template: ''})