Make class prop resolution faster (#28766)

`delete` causes an object (in V8, and maybe other engines) to deopt to a
dictionary instead of a class. Instead of `assign` + `delete`, manually
iterate over all the properties, like the JSX runtime does.
To avoid copying the object twice I moved the `ref` prop removal to come
before handling default props. If we already cloned the props to remove
`ref`, then we can skip cloning again to handle default props.

Author: acdlite

packages/react-reconciler/src/ReactFiberClassComponent.js

@@ -1251,32 +1251,39 @@ export function resolveClassComponentProps(
 ): Object{
 letnewProps=baseProps;
 
-// Resolve default props. Taken from old JSX runtime, where this used to live.
+if(enableRefAsProp){
+// Remove ref from the props object, if it exists.
+if('ref'inbaseProps){
+newProps=({}: any);
+for(constpropNameinbaseProps){
+if(propName!=='ref'){
+newProps[propName]=baseProps[propName];
+}
+}
+}
+}
+
+// Resolve default props.
 constdefaultProps=Component.defaultProps;
 if(
 defaultProps&&
 // If disableDefaultPropsExceptForClasses is true, we always resolve
 // default props here in the reconciler, rather than in the JSX runtime.
 (disableDefaultPropsExceptForClasses||!alreadyResolvedDefaultProps)
 ){
-newProps=assign({},newProps,baseProps);
+// We may have already copied the props object above to remove ref. If so,
+// we can modify that. Otherwise, copy the props object with Object.assign.
+if(newProps===baseProps){
+newProps=assign({},newProps,baseProps);
+}
+// Taken from old JSX runtime, where this used to live.
 for(constpropNameindefaultProps){
 if(newProps[propName]===undefined){
 newProps[propName]=defaultProps[propName];
 }
 }
 }
 
-if(enableRefAsProp){
-// Remove ref from the props object, if it exists.
-if('ref'innewProps){
-if(newProps===baseProps){
-newProps=assign({},newProps);
-}
-deletenewProps.ref;
-}
-}
-
 returnnewProps;
 }
 

packages/react-server/src/ReactFizzServer.js

@@ -1397,24 +1397,36 @@ export function resolveClassComponentProps(
 ): Object{
 letnewProps=baseProps;
 
-// Resolve default props. Taken from old JSX runtime, where this used to live.
-constdefaultProps=Component.defaultProps;
-if(defaultProps&&disableDefaultPropsExceptForClasses){
-newProps=assign({},newProps,baseProps);
-for(constpropNameindefaultProps){
-if(newProps[propName]===undefined){
-newProps[propName]=defaultProps[propName];
+if(enableRefAsProp){
+// Remove ref from the props object, if it exists.
+if('ref' inbaseProps){
+newProps=({}: any);
+for(constpropNameinbaseProps){
+if(propName!== 'ref'){
+newProps[propName]=baseProps[propName];
+}
 }
 }
 }
 
-if(enableRefAsProp){
-// Remove ref from the props object, if it exists.
-if('ref' innewProps){
-if(newProps===baseProps){
-newProps=assign({},newProps);
+// Resolve default props.
+constdefaultProps=Component.defaultProps;
+if(
+defaultProps&&
+// If disableDefaultPropsExceptForClasses is true, we always resolve
+// default props here, rather than in the JSX runtime.
+disableDefaultPropsExceptForClasses
+){
+// We may have already copied the props object above to remove ref. If so,
+// we can modify that. Otherwise, copy the props object with Object.assign.
+if(newProps===baseProps){
+newProps=assign({},newProps,baseProps);
+}
+// Taken from old JSX runtime, where this used to live.
+for(constpropNameindefaultProps){
+if(newProps[propName]===undefined){
+newProps[propName]=defaultProps[propName];
 }
-deletenewProps.ref;
 }
 }