Reduce branching. Make assignment more consistent

Author: nhunzaker

packages/react-dom/src/__tests__/ReactDOMInput-test.js

@@ -1593,7 +1593,7 @@ describe('ReactDOMInput', () => {
       var node = container.firstChild;
 
       expect(node.value).toBe('');
-      expect(node.getAttribute('value')).toBe(null);
+      expect(node.getAttribute('value')).toBe('');
     });
 
     it('does not update the value to a Symbol', function() {
@@ -1612,7 +1612,7 @@ describe('ReactDOMInput', () => {
       var node = container.firstChild;
 
       expect(node.value).toBe('');
-      expect(node.getAttribute('value')).toBe(null);
+      expect(node.getAttribute('value')).toBe('');
     });
 
     it('does not update defaultValue to a Symbol', function() {
@@ -1633,7 +1633,7 @@ describe('ReactDOMInput', () => {
       var node = container.firstChild;
 
       expect(node.value).toBe('');
-      expect(node.getAttribute('value')).toBe(null);
+      expect(node.getAttribute('value')).toBe('');
     });
 
     it('does not update the value to a function', function() {
@@ -1652,7 +1652,7 @@ describe('ReactDOMInput', () => {
       var node = container.firstChild;
 
       expect(node.value).toBe('');
-      expect(node.getAttribute('value')).toBe(null);
+      expect(node.getAttribute('value')).toBe('');
     });
 
     it('does not update defaultValue to a function', function() {

packages/react-dom/src/client/ReactDOMFiberInput.js

@@ -118,11 +118,17 @@ export function initWrapperState(element: Element, props: Object) {
   }
 
   var defaultValue = props.defaultValue == null ? '' : props.defaultValue;
+  var initialValue = props.value != null ? props.value : defaultValue;
   var node = ((element: any): InputWithWrapperState);
+
+  if (!shouldSetAttribute('value', initialValue)) {
+    initialValue = '';
+  }
+
   node._wrapperState = {
     initialChecked:
       props.checked != null ? props.checked : props.defaultChecked,
-    initialValue: props.value != null ? props.value : defaultValue,
+    initialValue: initialValue,
     controlled: isControlled(props),
   };
 }
@@ -200,11 +206,11 @@ export function updateWrapper(element: Element, props: Object) {
     } else if (node.value !== '' + value) {
       node.value = '' + value;
     }
+  }
+
+  if (props.hasOwnProperty('value')) {
     synchronizeDefaultValue(node, props.type, value);
-  } else if (
-    props.hasOwnProperty('value') ||
-    props.hasOwnProperty('defaultValue')
-  ) {
+  } else if (props.hasOwnProperty('defaultValue')) {
     synchronizeDefaultValue(node, props.type, defaultValue);
   }
 
@@ -215,21 +221,18 @@ export function updateWrapper(element: Element, props: Object) {
 
 export function postMountWrapper(element: Element, props: Object) {
   var node = ((element: any): InputWithWrapperState);
-  var initialValue = node._wrapperState.initialValue;
 
-  if (props.value != null || props.defaultValue != null) {
+  if (props.hasOwnProperty('value') || props.hasOwnProperty('defaultValue')) {
     // Do not assign value if it is already set. This prevents user text input
     // from being lost during SSR hydration.
-    if (node.value === '' && shouldSetAttribute('value', initialValue)) {
-      node.value = '' + initialValue;
+    if (node.value === '') {
+      node.value = '' + node._wrapperState.initialValue;
     }
 
     // value must be assigned before defaultValue. This fixes an issue where the
     // visually displayed value of date inputs disappears on mobile Safari and Chrome:
     // https://github.com/facebook/react/issues/7233
-    if (shouldSetAttribute('value', initialValue)) {
-      node.defaultValue = '' + initialValue;
-    }
+    node.defaultValue = '' + node._wrapperState.initialValue;
   }
 
   // Normally, we'd just do `node.checked = node.checked` upon initial mount, less this bug
@@ -320,10 +323,10 @@ export function synchronizeDefaultValue(
     type !== 'number' ||
     node.ownerDocument.activeElement !== node
   ) {
-    var nextValue =
-      '' + (value == null ? node._wrapperState.initialValue : value);
-    if (nextValue !== node.defaultValue) {
-      node.defaultValue = nextValue;
+    if (value == null) {
+      node.defaultValue = '' + node._wrapperState.initialValue;
+    } else if (node.defaultValue !== '' + value) {
+      node.defaultValue = '' + value;
     }
   }
 }