Repository: facebook/react
Pull request: Allow functions to be passed to custom element setters

## Summary

This is part of the new custom element features that were implemented
here: https://github.com/facebook/react/commit/24dd07bd269590ee5024b7f0f1906887d256ea86
This PR will only make a difference when the
enableCustomElementPropertySupport flag is enabled.

When a custom element has a setter for a property and passes the `in`
heuristic, the value passed to the react property should be assigned
directly to the custom element's property, regardless of the type of the
value. However, it was discovered that this isn't working with
functions. This patch makes it work with functions.

Fixes https://github.com/facebook/react/issues/23041

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## How did you test this change?

I added a test in DOMPropertyOperations-test.js

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Changed files:
filename: packages/react-dom/src/__tests__/DOMPropertyOperations-test.js
patch: @@ -504,6 +504,35 @@ describe('DOMPropertyOperations', () => {
       expect(customElement.foo).toBe('two');
       expect(customElement.getAttribute('foo')).toBe('one');
     });
+
+    // @gate enableCustomElementPropertySupport
+    it('custom element properties should accept functions', () => {
+      const container = document.createElement('div');
+      document.body.appendChild(container);
+      ReactDOM.render(<my-custom-element />, container);
+      const customElement = container.querySelector('my-custom-element');
+
+      // Install a setter to activate the `in` heuristic
+      Object.defineProperty(customElement, 'foo', {
+        set: function(x) {
+          this._foo = x;
+        },
+        get: function() {
+          return this._foo;
+        },
+      });
+      function myFunction() {
+        return 'this is myFunction';
+      }
+      ReactDOM.render(<my-custom-element foo={myFunction} />, container);
+      expect(customElement.foo).toBe(myFunction);
+
+      // Also remove and re-add the property for good measure
+      ReactDOM.render(<my-custom-element />, container);
+      expect(customElement.foo).toBe(null);
+      ReactDOM.render(<my-custom-element foo={myFunction} />, container);
+      expect(customElement.foo).toBe(myFunction);
+    });
   });
 
   describe('deleteValueForProperty', () => {

filename: packages/react-dom/src/client/DOMPropertyOperations.js
patch: @@ -184,10 +184,6 @@ export function setValueForProperty(
     }
   }
 
-  if (shouldRemoveAttribute(name, value, propertyInfo, isCustomComponentTag)) {
-    value = null;
-  }
-
   if (
     enableCustomElementPropertySupport &&
     isCustomComponentTag &&
@@ -197,6 +193,10 @@ export function setValueForProperty(
     return;
   }
 
+  if (shouldRemoveAttribute(name, value, propertyInfo, isCustomComponentTag)) {
+    value = null;
+  }
+
   // If the prop isn't in the special list, treat it as a simple attribute.
   if (isCustomComponentTag || propertyInfo === null) {
     if (isAttributeNameSafe(name)) {